bash.htmlTutorials - udel.eduudel.edu/~weiher/pdf/bash.pdf · bash_man_page Page 2 of 63 If the -i...

bash_man_page of 63

http://pegasus.rutgers.edu/~elflord/unix/bash.htmlTutorialsUseful information mostly written by me, the conspicuous exception being the bash manpage ...

Intro to UnixUNIX command summarygrep tutorial powerful search toolsed tutorial scripts to edit text filesAutofs in Linux automatically mounting removable mediaprocmail tutorial well known email filterbash manpage the man page for the bash shell. Warning: this is long (~210k)

BASH(1) �1998 Apr 1� BASH(1)

Index

NAMEbash - GNU Bourne-Again SHell

SYNOPSISbash [options] [file]

COPYRIGHTBash is Copyright © 1989, 1991, 1993, 1995, 1996 by the Free Software Foundation, Inc.

DESCRIPTIONBash is an sh-compatible command language interpreter that executes commands read from thestandard input or from a file. Bash also incorporates useful features from the Korn and C shells(ksh and csh).

Bash is intended to be a conformant implementation of the IEEE POSIX Shell and Toolsspecification (IEEE Working Group 1003.2).

OPTIONSIn addition to the single-character shell options documented in the description of the set builtincommand, bash interprets the following options when it is invoked:-c string

If the -c option is present, then commands are read from string. If there are arguments afterthe string, they are assigned to the positional parameters, starting with $0.

-rIf the -r option is present, the shell becomes restricted (see RESTRICTED SHELL below).

-i

bash_man_page of 63

If the -i option is present, the shell is interactive.-s

If the -s option is present, or if no arguments remain after option processing, then commandsare read from the standard input. This option allows the positional parameters to be setwhen invoking an interactive shell.

-DA list of all double-quoted strings preceded by $ is printed on the standard ouput. These arethe strings that are subject to language translation when the current locale is not C orPOSIX. This implies the -n option; no commands will be executed.

--A -- signals the end of options and disables further option processing. Any arguments afterthe -- are treated as filenames and arguments. An argument of - is equivalent to --.

Bash also interprets a number of multi-character options. These options must appear on thecommand line before the single-character options in order for them to be recognized.

--dump-po-stringsEquivalent to -D, but the output is in the GNU gettext po (portable object) file format.

--dump-stringsEquivalent to -D.

--helpDisplay a usage message on standard output and exit successfully.

--loginMake bash act as if it had been invoked as a login shell (see INVOCATION below).

--noeditingDo not use the GNU readline library to read command lines if interactive.

--noprofileDo not read either the system-wide startup file /etc/profile or any of the personalinitialization files ~/.bash_profile, ~/.bash_login, or ~/.profile. By default, bash reads thesefiles when it is invoked as a login shell (see INVOCATION below).

--norcDo not read and execute the personal initialization file ~/.bashrc if the shell is interactive.This option is on by default if the shell is invoked as sh.

--posixChange the behavior of bash where the default operation differs from the POSIX 1003.2standard to match the standard.

--rcfile fileExecute commands from file instead of the standard personal initialization file ~/.bashrc ifthe shell is interactive (see INVOCATION below).

--restrictedThe shell becomes restricted (see RESTRICTED SHELL below).

--verboseEquivalent to -v.

--versionShow version information for this instance of bash on the standard output and exitsuccessfully.

ARGUMENTSIf arguments remain after option processing, and neither the -c nor the -s option has been supplied,the first argument is assumed to be the name of a file containing shell commands. If bash is invokedin this fashion, $0 is set to the name of the file, and the positional parameters are set to theremaining arguments. Bash reads and executes commands from this file, then exits. Bash's exitstatus is the exit status of the last command executed in the script. If no commands are executed, theexit status is 0.

bash_man_page of 63

INVOCATIONA login shell is one whose first character of argument zero is a -, or one started with the --loginoption.

An interactive shell is one whose standard input and output are both connected to terminals (asdetermined by isatty(3)), or one started with the -i option. PS1 is set and $- includes i if bash isinteractive, allowing a shell script or a startup file to test this state.

The following paragraphs describe how bash executes its startup files. If any of the files exist butcannot be read, bash reports an error. Tildes are expanded in file names as described below underTilde Expansion in the EXPANSION section.

When bash is invoked as an interactive login shell, it first reads and executes commands from thefile /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login,and ~/.profile, in that order, and reads and executes commands from the first one that exists and isreadable. The --noprofile option may be used when the shell is started to inhibit this behavior.

When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if itexists.

When an interactive shell that is not a login shell is started, bash reads and executes commandsfrom ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile fileoption will force bash to read and execute commands from file instead of ~/.bashrc.

When bash is started non-interactively, to run a shell script, for example, it looks for the variableBASH_ENV in the environment, expands its value if it appears there, and uses the expanded value asthe name of a file to read and execute. Bash behaves as if the following command were executed:

if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi

but the value of the PATH variable is not used to search for the file name.

If bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions ofsh as closely as possible, while conforming to the POSIX standard as well. When invoked as aninteractive login shell, it first attempts to read and execute commands from /etc/profile and~/.profile, in that order. The --noprofile option may be used to inhibit this behavior. When invokedas an interactive shell with the name sh, bash looks for the variable ENV, expands its value if it isdefined, and uses the expanded value as the name of a file to read and execute. Since a shell invokedas sh does not attempt to read and execute commands from any other startup files, the --rcfileoption has no effect. A non-interactive shell invoked with the name sh does not attempt to read anystartup files. When invoked as sh, bash enters posix mode after the startup files are read.

When bash is started in posix mode, as with the --posix command line option, it follows the POSIXstandard for startup files. In this mode, interactive shells expand the ENV variable and commandsare read and executed from the file whose name is the expanded value. No other startup files areread.

Bash attempts to determine when it is being run by the remote shell daemon, usually rshd. If bashdetermines it is being run by rshd, it reads and executes commands from ~/.bashrc, if that file existsand is readable. It will not do this if invoked as sh. The --norc option may be used to inhibit thisbehavior, and the --rcfile option may be used to force another file to be read, but rshd does notgenerally invoke the shell with those options or allow them to be specified.

bash_man_page of 63

DEFINITIONSThe following definitions are used throughout the rest of this document.

blankA space or tab.

wordA sequence of characters considered as a single unit by the shell. Also known as a token.

nameA word consisting only of alphanumeric characters and underscores, and beginning with analphabetic character or an underscore. Also referred to as an identifier.

metacharacterA character that, when unquoted, separates words. One of the following:

| & ; ( ) < > space tab

control operatorA token that performs a control function. It is one of the following symbols:

|| & && ; ;; ( ) | <newline>

RESERVED WORDSReserved words are words that have a special meaning to the shell. The following words arerecognized as reserved when unquoted and either the first word of a simple command (see SHELLGRAMMAR below) or the third word of a case or for command:

! case do done elif else esac fi for function if in select then until while { } time [[ ]]

SHELL GRAMMAR

Simple Commands

A simple command is a sequence of optional variable assignments followed by blank-separatedwords and redirections, and terminated by a control operator. The first word specifies the commandto be executed. The remaining words are passed as arguments to the invoked command.

The return value of a simple command is its exit status, or 128+n if the command is terminated bysignal n.

Pipelines

A pipeline is a sequence of one or more commands separated by the character |. The format for apipeline is:

bash_man_page of 63

[time [-p]] [ ! ] command [ | command2 ... ]

The standard output of command is connected to the standard input of command2. This connectionis performed before any redirections specified by the command (see REDIRECTION below).

If the reserved word ! precedes a pipeline, the exit status of that pipeline is the logical NOT of theexit status of the last command. Otherwise, the status of the pipeline is the exit status of the lastcommand. The shell waits for all commands in the pipeline to terminate before returning a value.

If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumedby its execution are reported when the pipeline terminates. The -p option changes the output formatto that specified by POSIX. The TIMEFORMAT variable may be set to a format string that specifieshow the timing information should be displayed; see the description of TIMEFORMAT under ShellVariables below.

Each command in a pipeline is executed as a separate process (i.e., in a subshell).

Lists

A list is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||, andoptionally terminated by one of ;, &, or <newline>.

Of these list operators, && and || have equal precedence, followed by ; and &, which have equalprecedence.

If a command is terminated by the control operator &, the shell executes the command in thebackground in a subshell. The shell does not wait for the command to finish, and the return status is0. Commands separated by a ; are executed sequentially; the shell waits for each command toterminate in turn. The return status is the exit status of the last command executed.

The control operators && and || denote AND lists and OR lists, respectively. An AND list has theform

command && command2

command2 is executed if, and only if, command returns an exit status of zero.

An OR list has the form

command || command2

command2 is executed if and only if command returns a non-zero exit status. The return status ofAND and OR lists is the exit status of the last command executed in the list.

Compound Commands

A compound command is one of the following:

(list)list is executed in a subshell. Variable assignments and builtin commands that affect theshell's environment do not remain in effect after the command completes. The return statusis the exit status of list.

{ list; }

bash_man_page of 63

list is simply executed in the current shell environment. list must be terminated with anewline or semicolon. This is known as a group command. The return status is the exitstatus of list.

((expression))The expression is evaluated according to the rules described below underARITHMETICEVALUATION. If the value of the expression is non-zero, the return status is 0;otherwise the return status is 1. This is exactly equivalent to let "expression".

[[ expression ]]Return a status of 0 or 1 depending on the evaluation of the conditional expressionexpression. Expressions are composed of the primaries described below underCONDITIONALEXPRESSIONS. Word splitting and pathname expansion are not performed on thewords between the [[ and ]]; tilde expansion, parameter and variable expansion, arithmeticexpansion, command substitution, process substitution, and quote removal are performed.

When the == and != operators are used, the string to the right of the operator is considered apattern and matched according to the rules described below under Pattern Matching. Thereturn value is 0 if the string matches or does not match the pattern, respectively, and 1otherwise. Any part of the pattern may be quoted to force it to be matched as a string.

Expressions may be combined using the following operators, listed in decreasing order ofprecedence:

( expression )Returns the value of expression. This may be used to override the normal precedence ofoperators.! expressionTrue if expression is false.expression1 && expression2True if both expression1 and expression2 are true.expression1 || expression2True if either expression1 or expression2 is true.

The && and || operators do not execute expression2 if the value of expression1 is sufficient todetermine the return value of the entire conditional expression.

for name [ in word; ] do list ; doneThe list of words following in is expanded, generating a list of items. The variable name isset to each element of this list in turn, and list is executed each time. If the in word isomitted, the for command executes list once for each positional parameter that is set (seePARAMETERS below). The return status is the exit status of the last command that executes. Ifthe expansion of the items following in results in an empty list, no commands are executed,and the return status is 0.

select name [ in word; ] do list ; doneThe list of words following in is expanded, generating a list of items. The set of expandedwords is printed on the standard error, each preceded by a number. If the in word is omitted,the positional parameters are printed (see PARAMETERS below). The PS3 prompt is thendisplayed and a line read from the standard input. If the line consists of a numbercorresponding to one of the displayed words, then the value of name is set to that word. If theline is empty, the words and prompt are displayed again. If EOF is read, the commandcompletes. Any other value read causes name to be set to null. The line read is saved in thevariable REPLY. The list is executed after each selection until a break or return commandis executed. The exit status of select is the exit status of the last command executed in list,or zero if no commands were executed.

case word in [ ( pattern [ | pattern ]A case command first expands word, and tries to match it against each pattern in turn,using the same matching rules as for pathname expansion (see Pathname Expansionbelow). When a match is found, the corresponding list is executed. After the first match, no

bash_man_page of 63

subsequent matches are attempted. The exit status is zero if no pattern matches. Otherwise,it is the exit status of the last command executed in list.

if list; then list; [ elif list; then list; ] ... [ else list; ] fiThe if list is executed. If its exit status is zero, the then list is executed. Otherwise, each eliflist is executed in turn, and if its exit status is zero, the corresponding then list is executedand the command completes. Otherwise, the else list is executed, if present. The exit statusis the exit status of the last command executed, or zero if no condition tested true.while list; do list; done

until list; do list; doneThe while command continuously executes the do list as long as the last command in listreturns an exit status of zero. The until command is identical to the while command, exceptthat the test is negated; the do list is executed as long as the last command in list returns anon-zero exit status. The exit status of the while and until commands is the exit status ofthe last do list command executed, or zero if none was executed.

[ function ] name () { list; }This defines a function named name. The body of the function is the list of commandsbetween { and }. This list is executed whenever name is specified as the name of a simplecommand. The exit status of a function is the exit status of the last command executed in thebody. (See FUNCTIONS below.)

COMMENTSIn a non-interactive shell, or an interactive shell in which the interactive_comments option to theshopt builtin is enabled (see SHELL BUILTIN COMMANDS below), a word beginning with # causes thatword and all remaining characters on that line to be ignored. An interactive shell without theinteractive_comments option enabled does not allow comments. The interactive_commentsoption is on by default in interactive shells.

QUOTINGQuoting is used to remove the special meaning of certain characters or words to the shell. Quotingcan be used to disable special treatment for special characters, to prevent reserved words from beingrecognized as such, and to prevent parameter expansion.

Each of the metacharacters listed above under DEFINITIONS has special meaning to the shell andmust be quoted if they are to represent themselves. There are three quoting mechanisms: the escapecharacter, single quotes, and double quotes.

A non-quoted backslash (\) is the escape character. It preserves the literal value of the nextcharacter that follows, with the exception of <newline>. If a \<newline> pair appears, and thebackslash is not itself quoted, the \<newline> is treated as a line continuation (that is, it is removedfrom the input stream and effectively ignored).

Enclosing characters in single quotes preserves the literal value of each character within the quotes.A single quote may not occur between single quotes, even when preceded by a backslash.

Enclosing characters in double quotes preserves the literal value of all characters within the quotes,with the exception of $, `, and \. The characters $ and ` retain their special meaning within doublequotes. The backslash retains its special meaning only when followed by one of the followingcharacters: $, `, ", \, or <newline>. A double quote may be quoted within double quotes by precedingit with a backslash.

bash_man_page of 63

The special parameters * and @ have special meaning when in double quotes (see PARAMETERSbelow).

Words of the form $'string' are treated specially. The word expands to string, with backslash-escapedcharacters replaced as specifed by the ANSI C standard. Backslash escape sequences, if present, aredecoded as follows:

\aalert (bell)\bbackspace\ean escape character\fform feed\nnew line\rcarriage return\thorizontal tab\vvertical tab\\backslash\nnnthe character whose ASCII code is the octal value nnn (one to three digits)\xnnnthe character whose ASCII code is the hexadecimal value nnn (one to three digits)

The translated result is single-quoted, as if the dollar sign had not been present.

A double-quoted string preceded by a dollar sign ($) will cause the string to be translated accordingto the current locale. If the current locale is C or POSIX, the dollar sign is ignored. If the string istranslated and replaced, the replacement is double-quoted.

PARAMETERSA parameter is an entity that stores values. It can be a name, a number, or one of the specialcharacters listed below under Special Parameters. For the shell's purposes, a variable is aparameter denoted by a name.

A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable isset, it may be unset only by using the unset builtin command (see SHELL BUILTIN COMMANDS below).

A variable may be assigned to by a statement of the form

name=[value]

If value is not given, the variable is assigned the null string. All values undergo tilde expansion,parameter and variable expansion, string expansion, command substitution, arithmetic expansion,and quote removal (see EXPANSION below). If the variable has its integer attribute set (see declarebelow in SHELLBUILTINCOMMANDS) then value is subject to arithmetic expansion even if the $((...))expansion is not used (see Arithmetic Expansion below). Word splitting is not performed, with the

bash_man_page of 63

exception of "$@" as explained below under Special Parameters. Pathname expansion is notperformed.

Positional Parameters

A positional parameter is a parameter denoted by one or more digits, other than the single digit 0.Positional parameters are assigned from the shell's arguments when it is invoked, and may bereassigned using the set builtin command. Positional parameters may not be assigned to withassignment statements. The positional parameters are temporarily replaced when a shell function isexecuted (see FUNCTIONS below).

When a positional parameter consisting of more than a single digit is expanded, it must be enclosedin braces (see EXPANSION below).

Special Parameters

The shell treats several parameters specially. These parameters may only be referenced; assignmentto them is not allowed.

*Expands to the positional parameters, starting from one. When the expansion occurs withindouble quotes, it expands to a single word with the value of each parameter separated by thefirst character of the IFS special variable. That is, "$*" is equivalent to "$1c$2c...", where c isthe first character of the value of the IFS variable. If IFS is unset, the parameters areseparated by spaces. If IFS is null, the parameters are joined without intervening separators.

@Expands to the positional parameters, starting from one. When the expansion occurs withindouble quotes, each parameter expands to a separate word. That is, "$@" is equivalent to "$1""$2" ... When there are no positional parameters, "$@" and $@ expand to nothing (i.e., theyare removed).

#Expands to the number of positional parameters in decimal.

?Expands to the status of the most recently executed foreground pipeline.

-Expands to the current option flags as specified upon invocation, by the set builtin command,or those set by the shell itself (such as the -i option).

$Expands to the process ID of the shell. In a () subshell, it expands to the process ID of thecurrent shell, not the subshell.

!Expands to the process ID of the most recently executed background (asynchronous)command.

0Expands to the name of the shell or shell script. This is set at shell initialization. If bash isinvoked with a file of commands, $0 is set to the name of that file. If bash is started with the-c option, then $0 is set to the first argument after the string to be executed, if one is present.Otherwise, it is set to the file name used to invoke bash, as given by argument zero.

_At shell startup, set to the absolute file name of the shell or shell script being executed aspassed in the argument list. Subsequently, expands to the last argument to the previouscommand, after expansion. Also set to the full file name of each command executed andplaced in the environment exported to that command. When checking mail, this parameterholds the name of the mail file currently being checked.

bash_man_page of 63

Shell Variables

The following variables are set by the shell:

PPIDThe process ID of the shell's parent. This variable is readonly.

PWDThe current working directory as set by the cd command.

OLDPWDThe previous working directory as set by the cd command.

REPLYSet to the line of input read by the read builtin command when no arguments are supplied.

UIDExpands to the user ID of the current user, initialized at shell startup. This variable isreadonly.

EUIDExpands to the effective user ID of the current user, initialized at shell startup. This variableis readonly.

GROUPSAn array variable containing the list of groups of which the current user is a member. Thisvariable is readonly.

BASHExpands to the full file name used to invoke this instance of bash.

BASH_VERSIONExpands to a string describing the version of this instance of bash.

BASH_VERSINFOA readonly array variable whose members hold version information for this instance of bash.The values assigned to the array members are as follows:BASH_VERSINFO[0]The major version number (the release).BASH_VERSINFO[1]The minor version number (the version).BASH_VERSINFO[2]The patch level.BASH_VERSINFO[3]The build version.BASH_VERSINFO[4]The release status (e.g., beta1).BASH_VERSINFO[5]The value of MACHTYPE.

SHLVLIncremented by one each time an instance of bash is started.

RANDOMEach time this parameter is referenced, a random integer between 0 and 32767 is generated.The sequence of random numbers may be initialized by assigning a value to RANDOM. IfRANDOM is unset, it loses its special properties, even if it is subsequently reset.

SECONDSEach time this parameter is referenced, the number of seconds since shell invocation isreturned. If a value is assigned to SECONDS, the value returned upon subsequent references isthe number of seconds since the assignment plus the value assigned. If SECONDS is unset, itloses its special properties, even if it is subsequently reset.

LINENOEach time this parameter is referenced, the shell substitutes a decimal number representingthe current sequential line number (starting with 1) within a script or function. When not ina script or function, the value substituted is not guaranteed to be meaningful. If LINENO isunset, it loses its special properties, even if it is subsequently reset.

HISTCMD

bash_man_page of 63

The history number, or index in the history list, of the current command. If HISTCMD is unset,it loses its special properties, even if it is subsequently reset.

DIRSTACKAn array variable (see Arrays below) containing the current contents of the directory stack.Directories appear in the stack in the order they are displayed by the dirs builtin. Assigningto members of this array variable may be used to modify directories already in the stack, butthe pushd and popd builtins must be used to add and remove directories. Assignment tothis variable will not change the current directory. If DIRSTACK is unset, it loses its specialproperties, even if it is subsequently reset.

PIPESTATUSAn array variable (see Arrays below) containing a list of exit status values from theprocesses in the most-recently-executed foreground pipeline (which may contain only a singlecommand).

OPTARGThe value of the last option argument processed by the getopts builtin command (see SHELLBUILTIN COMMANDS below).

OPTINDThe index of the next argument to be processed by the getopts builtin command (see SHELLBUILTIN COMMANDS below).

HOSTNAMEAutomatically set to the name of the current host.

HOSTTYPEAutomatically set to a string that uniquely describes the type of machine on which bash isexecuting. The default is system-dependent.

OSTYPEAutomatically set to a string that describes the operating system on which bash is executing.The default is system-dependent.

MACHTYPEAutomatically set to a string that fully describes the system type on which bash is executing,in the standard GNU cpu-company-system format. The default is system-dependent.

SHELLOPTSA colon-separated list of enabled shell options. Each word in the list is a valid argument forthe -o option to the set builtin command (see SHELL BUILTIN COMMANDS below). The optionsappearing in SHELLOPTS are those reported as on by set -o. If this variable is in theenvironment when bash starts up, each shell option in the list will be enabled before readingany startup files. This variable is read-only.

The following variables are used by the shell. In some cases, bash assigns a default value to avariable; these cases are noted below.

IFSThe Internal Field Separator that is used for word splitting after expansion and to split linesinto words with the read builtin command. The default value is ``<space><tab><newline>''.

PATHThe search path for commands. It is a colon-separated list of directories in which the shelllooks for commands (see COMMAND EXECUTION below). The default path is system-dependent,and is set by the administrator who installs bash. A common value is``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.''.

HOMEThe home directory of the current user; the default argument for the cd builtin command.The value of this variable is also used when performing tilde expansion.

CDPATHThe search path for the cd command. This is a colon-separated list of directories in which theshell looks for destination directories specified by the cd command. A sample value is``.:~:/usr''.

BASH_ENVIf this parameter is set when bash is executing a shell script, its value is interpreted as afilename containing commands to initialize the shell, as in ~/.bashrc. The value of BASH_ENV

bash_man_page of 63

is subjected to parameter expansion, command substitution, and arithmetic expansion beforebeing interpreted as a file name. PATH is not used to search for the resultant file name.

MAILIf this parameter is set to a file name and the MAILPATH variable is not set, bash informs theuser of the arrival of mail in the specified file.

MAILCHECKSpecifies how often (in seconds) bash checks for mail. The default is 60 seconds. When it istime to check for mail, the shell does so before displaying the primary prompt. If this variableis unset, the shell disables mail checking.

MAILPATHA colon-separated list of file names to be checked for mail. The message to be printed whenmail arrives in a particular file may be specified by separating the file name from themessage with a `?'. When used in the text of the message, $_ expands to the name of thecurrent mailfile. Example:

MAILPATH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'

Bash supplies a default value for this variable, but the location of the user mail files that ituses is system dependent (e.g., /usr/spool/mail/$USER).

PS1The value of this parameter is expanded (see PROMPTING below) and used as the primaryprompt string. The default value is ``\s-\v\$ ''.

PS2The value of this parameter is expanded as with PS1 and used as the secondary promptstring. The default is ``> ''.

PS3The value of this parameter is used as the prompt for the select command (see SHELLGRAMMAR above).

PS4The value of this parameter is expanded as with PS1 and the value is printed before eachcommand bash displays during an execution trace. The first character of PS4 is replicatedmultiple times, as necessary, to indicate multiple levels of indirection. The default is ``+ ''.

TIMEFORMATThe value of this parameter is used as a format string specifying how the timing informationfor pipelines prefixed with the time reserved word should be displayed. The % characterintroduces an escape sequence that is expanded to a time value or other information. Theescape sequences and their meanings are as follows; the braces denote optional portions.%%A literal %.%[p][l]RThe elapsed time in seconds.%[p][l]UThe number of CPU seconds spent in user mode.%[p][l]SThe number of CPU seconds spent in system mode.%PThe CPU percentage, computed as (%U + %S) / %R.The optional p is a digit specifying the precision, the number of fractional digits after adecimal point. A value of 0 causes no decimal point or fraction to be output. At most threeplaces after the decimal point may be specified; values of p greater than 3 are changed to 3. Ifp is not specified, the value 3 is used.The optional l specifies a longer format, including minutes, of the form MMmSS.FFs. Thevalue of p determines whether or not the fraction is included.If this variable is not set, bash acts as if it had the value$'\nreal\t%3lR\nuser\t%3lU\nsys %3lS'. If the value is null, no timing information isdisplayed. A trailing newline is added when the format string is displayed.

HISTSIZE

bash_man_page of 63

The number of commands to remember in the command history (see HISTORY below). Thedefault value is 500.

HISTFILEThe name of the file in which command history is saved (see HISTORY below). The defaultvalue is ~/.bash_history. If unset, the command history is not saved when an interactiveshell exits.

HISTFILESIZEThe maximum number of lines contained in the history file. When this variable is assigned avalue, the history file is truncated, if necessary, to contain no more than that number oflines. The default value is 500. The history file is also truncated to this size after writing itwhen an interactive shell exits.

OPTERRIf set to the value 1, bash displays error messages generated by the getopts builtincommand (see SHELL BUILTIN COMMANDS below). OPTERR is initialized to 1 each time the shellis invoked or a shell script is executed.

LANGUsed to determine the locale category for any category not specifically selected with avariable starting with LC_.

LC_ALLThis variable overrides the value of LANG and any other LC_ variable specifying a localecategory.

LC_COLLATEThis variable determines the collation order used when sorting the results of pathnameexpansion, and determines the behavior of range expressions, equivalence classes, andcollating sequences within pathname expansion and pattern matching.

LC_CTYPEThis variable determines the interpretation of characters and the behavior of characterclasses within pathname expansion and pattern matching.

LC_MESSAGESThis variable determines the locale used to translate double-quoted strings preceded by a $.

PROMPT_COMMANDIf set, the value is executed as a command prior to issuing each primary prompt.

IGNOREEOFControls the action of an interactive shell on receipt of an EOF character as the sole input. Ifset, the value is the number of consecutive EOF characters which must be typed as the firstcharacters on an input line before bash exits. If the variable exists but does not have anumeric value, or has no value, the default value is 10. If it does not exist, EOF signifies theend of input to the shell.

TMOUTIf set to a value greater than zero, the value is interpreted as the number of seconds to waitfor input after issuing the primary prompt. Bash terminates after waiting for that number ofseconds if input does not arrive.

FCEDITThe default editor for the fc builtin command.

FIGNOREA colon-separated list of suffixes to ignore when performing filename completion (seeREADLINE below). A filename whose suffix matches one of the entries in FIGNORE is excludedfrom the list of matched filenames. A sample value is ``.o:~''.

GLOBIGNOREA colon-separated list of patterns defining the set of filenames to be ignored by pathnameexpansion. If a filename matched by a pathname expansion pattern also matches one of thepatterns in GLOBIGNORE, it is removed from the list of matches.

INPUTRCThe filename for the readline startup file, overriding the default of ~/.inputrc (see READLINEbelow).

HISTCONTROLIf set to a value of ignorespace, lines which begin with a space character are not entered onthe history list. If set to a value of ignoredups, lines matching the last history line are not

bash_man_page of 63

entered. A value of ignoreboth combines the two options. If unset, or if set to any other valuethan those above, all lines read by the parser are saved on the history list, subject to thevalue of HISTIGNORE. This variable's function is superseded by HISTIGNORE. Thesecond and subsequent lines of a multi-line compound command are not tested, and areadded to the history regardless of the value of HISTCONTROL.

HISTIGNOREA colon-separated list of patterns used to decide which command lines should be saved on thehistory list. Each pattern is anchored at the beginning of the line and must fully specify theline (no implicit `*' is appended). Each pattern is tested against the line after the checksspecified by HISTCONTROL are applied. In addition to the normal shell pattern matchingcharacters, `&' matches the previous history line. `&' may be escaped using a backslash. Thebackslash is removed before attempting a match. The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the valueof HISTIGNORE.

histcharsThe two or three characters which control history expansion and tokenization (see HISTORYEXPANSION below). The first character is the history expansion character, the character whichsignals the start of a history expansion, normally `!'. The second character is the quicksubstitution character, which is used as shorthand for re-running the previous commandentered, substituting one string for another in the command. The default is `^'. The optionalthird character is the character which indicates that the remainder of the line is a commentwhen found as the first character of a word, normally `#'. The history comment charactercauses history substitution to be skipped for the remaining words on the line. It does notnecessarily cause the shell parser to treat the rest of the line as a comment.

HOSTFILEContains the name of a file in the same format as /etc/hosts that should be read when theshell needs to complete a hostname. The file may be changed interactively; the next timehostname completion is attempted bash adds the contents of the new file to the alreadyexisting database.

auto_resumeThis variable controls how the shell interacts with the user and job control. If this variable isset, single word simple commands without redirections are treated as candidates forresumption of an existing stopped job. There is no ambiguity allowed; if there is more thanone job beginning with the string typed, the job most recently accessed is selected. The nameof a stopped job, in this context, is the command line used to start it. If set to the value exact,the string supplied must match the name of a stopped job exactly; if set to substring, thestring supplied needs to match a substring of the name of a stopped job. The substring valueprovides functionality analogous to the %? job identifier (see JOB CONTROL below). If set toany other value, the supplied string must be a prefix of a stopped job's name; this providesfunctionality analogous to the % job identifier.

Arrays

Bash provides one-dimensional array variables. Any variable may be used as an array; the declarebuiltin will explicitly declare an array. There is no maximum limit on the size of an array, nor anyrequirement that members be indexed or assigned contiguously. Arrays are indexed using integersand are zero-based.

An array is created automatically if any variable is assigned to using the syntaxname[subscript]=value. The subscript is treated as an arithmetic expression that must evaluate to anumber greater than or equal to zero. To explicitly declare an array, use declare -a name (see SHELLBUILTIN COMMANDS below). declare -a name[subscript] is also accepted; the subscript is ignored.Attributes may be specified for an array variable using the declare and readonly builtins. Eachattribute applies to all members of an array.

bash_man_page of 63

Arrays are assigned to using compound assignments of the form name=(value1 ... valuen), whereeach value is of the form [subscript]=string. Only string is required. If the optional brackets andsubscript are supplied, that index is assigned to; otherwise the index of the element assigned is thelast index assigned to by the statement plus one. Indexing starts at zero. This syntax is also acceptedby the declare builtin. Individual array elements may be assigned to using thename[subscript]=value syntax introduced above.

Any element of an array may be referenced using ${name[subscript]}. The braces are required toavoid conflicts with pathname expansion. If subscript is @ or *, the word expands to all members ofname. These subscripts differ only when the word appears within double quotes. If the word isdouble-quoted, ${name[*]} expands to a single word with the value of each array member separatedby the first character of the IFS special variable, and ${name[@]} expands each element of name to aseparate word. When there are no array members, ${name[@]} expands to nothing. This is analogousto the expansion of the special parameters * and @ (see Special Parameters above).${#name[subscript]} expands to the length of ${name[subscript]}. If subscript is * or @, the expansionis the number of elements in the array. Referencing an array variable without a subscript isequivalent to referencing element zero.

The unset builtin is used to destroy arrays. unset name[subscript] destroys the array element atindex subscript. unset name, where name is an array, or unset name[subscript], where subscript is *or @, removes the entire array.

The declare, local, and readonly builtins each accept a -a option to specify an array. The readbuiltin accepts a -a option to assign a list of words read from the standard input to an array. The setand declare builtins display array values in a way that allows them to be reused as assignments.

EXPANSIONExpansion is performed on the command line after it has been split into words. There are sevenkinds of expansion performed: brace expansion, tilde expansion, parameter and variable expansion,command substitution, arithmetic expansion, word splitting, and pathname expansion.

The order of expansions is: brace expansion, tilde expansion, parameter, variable and arithmeticexpansion and command substitution (done in a left-to-right fashion), word splitting, and pathnameexpansion.

On systems that can support it, there is an additional expansion available: process substitution.

Only brace expansion, word splitting, and pathname expansion can change the number of words ofthe expansion; other expansions expand a single word to a single word. The only exceptions to thisare the expansions of "$@" and "${name[@]}" as explained above (see PARAMETERS).

Brace Expansion

Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism issimilar to pathname expansion, but the filenames generated need not exist. Patterns to be braceexpanded take the form of an optional preamble, followed by a series of comma-separated stringsbetween a pair of braces, followed by an optional postscript. The preamble is prefixed to each stringcontained within the braces, and the postscript is then appended to each resulting string, expandingleft to right.

Brace expansions may be nested. The results of each expanded string are not sorted; left to rightorder is preserved. For example, a{d,c,b}e expands into `ade ace abe'.

bash_man_page of 63

Brace expansion is performed before any other expansions, and any characters special to otherexpansions are preserved in the result. It is strictly textual. Bash does not apply any syntacticinterpretation to the context of the expansion or the text between the braces.

A correctly-formed brace expansion must contain unquoted opening and closing braces, and at leastone unquoted comma. Any incorrectly formed brace expansion is left unchanged. A { or , may bequoted with a backslash to prevent its being considered part of a brace expression.

This construct is typically used as shorthand when the common prefix of the strings to be generatedis longer than in the above example:

mkdir /usr/local/src/bash/{old,new,dist,bugs}

orchown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

Brace expansion introduces a slight incompatibility with historical versions of sh. sh does not treatopening or closing braces specially when they appear as part of a word, and preserves them in theoutput. Bash removes braces from words as a consequence of brace expansion. For example, a wordentered to sh as file{1,2} appears identically in the output. The same word is output as file1 file2after expansion by bash. If strict compatibility with sh is desired, start bash with the +B option ordisable brace expansion with the +B option to the set command (see SHELL BUILTIN COMMANDSbelow).

Tilde Expansion

If a word begins with an unquoted tilde character (`~'), all of the characters preceding the firstunquoted slash (or all characters, if there is no unquoted slash) are considered a tilde-prefix. If noneof the characters in the tilde-prefix are quoted, the characters in the tilde-prefix following the tildeare treated as a possible login name. If this login name is the null string, the tilde is replaced withthe value of the shell parameter HOME. If HOME is unset, the home directory of the user executing theshell is substituted instead. Otherwise, the tilde-prefix is replaced with the home directoryassociated with the specified login name.

If the tilde-prefix is a `~+', the value of the shell variable PWD replaces the tilde-prefix. If the tilde-prefix is a `~-', the value of the shell variable OLDPWD, if it is set, is substituted. If the charactersfollowing the tilde in the tilde-prefix consist of a number N, optionally prefixed by a `+' or a `-', thetilde-prefix is replaced with the corresponding element from the directory stack, as it would bedisplayed by the dirs builtin invoked with the tilde-prefix as an argument. If the charactersfollowing the tilde in the tilde-prefix consist of a number without a leading `+' or `-', `+' is assumed.

If the login name is invalid, or the tilde expansion fails, the word is unchanged.

Each variable assignment is checked for unquoted tilde-prefixes immediately following a : or =. Inthese cases, tilde expansion is also performed. Consequently, one may use file names with tildes inassignments to PATH, MAILPATH, and CDPATH, and the shell assigns the expanded value.

Parameter Expansion

The `$' character introduces parameter expansion, command substitution, or arithmetic expansion.The parameter name or symbol to be expanded may be enclosed in braces, which are optional butserve to protect the variable to be expanded from characters immediately following it which could beinterpreted as part of the name.

bash_man_page of 63

When braces are used, the matching ending brace is the first `}' not escaped by a backslash or withina quoted string, and not within an embedded arithmetic expansion, command substitution, orparamter expansion.

${parameter}The value of parameter is substituted. The braces are required when parameter is apositional parameter with more than one digit, or when parameter is followed by a characterwhich is not to be interpreted as part of its name.

If the first character of parameter is an exclamation point, a level of variable indirection isintroduced. Bash uses the value of the variable formed from the rest of parameter as the name of thevariable; this variable is then expanded and that value used in the rest of the substitution, ratherthan the value of parameter itself. This is known as indirect expansion.

In each of the cases below, word is subject to tilde expansion, parameter expansion, commandsubstitution, and arithmetic expansion. When not performing substring expansion, bash tests for aparameter that is unset or null; omitting the colon results in a test only for a parameter that isunset.

${parameter:-word}Use Default Values. If parameter is unset or null, the expansion of word is substituted.Otherwise, the value of parameter is substituted.

${parameter:=word}Assign Default Values. If parameter is unset or null, the expansion of word is assigned toparameter. The value of parameter is then substituted. Positional parameters and specialparameters may not be assigned to in this way.

${parameter:?word}Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or amessage to that effect if word is not present) is written to the standard error and the shell, ifit is not interactive, exits. Otherwise, the value of parameter is substituted.

${parameter:+word}Use Alternate Value. If parameter is null or unset, nothing is substituted, otherwise theexpansion of word is substituted.${parameter:offset}

${parameter:offset:length}Substring Expansion. Expands to up to length characters of parameter, starting at thecharacters specified by offset. If length is omitted, expands to the substring of parameter,starting at the character specified by offset. length and offset are arithmetic expressions (seeARITHMETIC EVALUATION below). length must evaluate to a number greater than or equal tozero. If offset evaluates to a number less than zero, the value is used as an offset from theend of the value of parameter. If parameter is @, the result is length positional parametersbeginning at offset. If parameter is an array name indexed by @ or *, the result is the lengthmembers of the array beginning with ${parameter[offset]}. Substring indexing is zero-basedunless the positional parameters are used, in which case the indexing starts at 1.

${#parameter}The length in characters of the value of parameter is substituted. If parameter is * or @, thevalue substituted is the number of positional parameters. If parameter is an array namesubscripted by * or @, the value substituted is the number of elements in the array.${parameter#word}

${parameter##word}The word is expanded to produce a pattern just as in pathname expansion. If the patternmatches the beginning of the value of parameter, then the result of the expansion is theexpanded value of parameter with the shortest matching pattern (the ``#'' case) or the longestmatching pattern (the ``##'' case) deleted. If parameter is @ or *, the pattern removaloperation is applied to each positional parameter in turn, and the expansion is the resultantlist. If parameter is an array variable subscripted with @ or *, the pattern removal operationis applied to each member of the array in turn, and the expansion is the resultant list.

bash_man_page of 63

${parameter%word}${parameter%%word}

The word is expanded to produce a pattern just as in pathname expansion. If the patternmatches a trailing portion of the expanded value of parameter, then the result of theexpansion is the expanded value of parameter with the shortest matching pattern (the ``%''case) or the longest matching pattern (the ``%%'' case) deleted. If parameter is @ or *, thepattern removal operation is applied to each positional parameter in turn, and the expansionis the resultant list. If parameter is an array variable subscripted with @ or *, the patternremoval operation is applied to each member of the array in turn, and the expansion is theresultant list.${parameter/pattern/string}

${parameter//pattern/string}The pattern is expanded to produce a pattern just as in pathname expansion. Parameter isexpanded and the longest match of pattern against its value is replaced with string. In thefirst form, only the first match is replaced. The second form causes all matches of pattern tobe replaced with string. If pattern begins with #, it must match at the beginning of string. Ifpattern begins with %, it must match at the end of string. If string is null, matches of patternare deleted and the / following pattern may be omitted. If parameter is @ or *, thesubstitution operation is applied to each positional parameter in turn, and the expansion isthe resultant list. If parameter is an array variable subscripted with @ or *, the substitutionoperation is applied to each member of the array in turn, and the expansion is the resultantlist.

Command Substitution

Command substitution allows the output of a command to replace the command name. There are twoforms:

$(command)

or`command`

Bash performs the expansion by executing command and replacing the command substitution withthe standard output of the command, with any trailing newlines deleted. Embedded newlines are notdeleted, but they may be removed during word splitting. The command substitution $(cat file) canbe replaced by the equivalent but faster $(< file).

When the old-style backquote form of substitution is used, backslash retains its literal meaningexcept when followed by $, `, or \. The first backquote not preceded by a backslash terminates thecommand substitution. When using the $(command) form, all characters between the parenthesesmake up the command; none are treated specially.

Command substitutions may be nested. To nest when using the backquoted form, escape the innerbackquotes with backslashes.

If the substitution appears within double quotes, word splitting and pathname expansion are notperformed on the results.

Arithmetic Expansion

Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of theresult. The format for arithmetic expansion is:

bash_man_page of 63

$((expression))

The expression is treated as if it were within double quotes, but a double quote inside theparentheses is not treated specially. All tokens in the expression undergo parameter expansion,string expansion, command substitution, and quote removal. Arithmetic substitutions may benested.

The evaluation is performed according to the rules listed below under ARITHMETICEVALUATION. Ifexpression is invalid, bash prints a message indicating failure and no substitution occurs.

Process Substitution

Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fdmethod of naming open files. It takes the form of <(list) or >(list). The process list is run with itsinput or output connected to a FIFO or some file in /dev/fd. The name of this file is passed as anargument to the current command as the result of the expansion. If the >(list) form is used, writingto the file will provide input for list. If the <(list) form is used, the file passed as an argument shouldbe read to obtain the output of list.

When available, process substitution is performed simultaneously with parameter and variableexpansion, command substitution, and arithmetic expansion.

Word Splitting

The shell scans the results of parameter expansion, command substitution, and arithmetic expansionthat did not occur within double quotes for word splitting.

The shell treats each character of IFS as a delimiter, and splits the results of the other expansionsinto words on these characters. If IFS is unset, or its value is exactly <space><tab><newline>, thedefault, then any sequence of IFS characters serves to delimit words. If IFS has a value other than thedefault, then sequences of the whitespace characters space and tab are ignored at the beginningand end of the word, as long as the whitespace character is in the value of IFS (an IFS whitespacecharacter). Any character in IFS that is not IFS whitespace, along with any adjacent IFS whitespacecharacters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter. Ifthe value of IFS is null, no word splitting occurs.

Explicit null arguments ("" or '') are retained. Unquoted implicit null arguments, resulting from theexpansion of parameters that have no values, are removed. If a parameter with no value is expandedwithin double quotes, a null argument results and is retained.

Note that if no expansion occurs, no splitting is performed.

Pathname Expansion

After word splitting, unless the -f option has been set, bash scans each word for the characters *, ?,(, and [. If one of these characters appears, then the word is regarded as a pattern, and replaced withan alphabetically sorted list of file names matching the pattern. If no matching file names are found,and the shell option nullglob is disabled, the word is left unchanged. If the nullglob option is set,and no matches are found, the word is removed. If the shell option nocaseglob is enabled, the matchis performed without regard to the case of alphabetic characters. When a pattern is used forpathname expansion, the character ``.'' at the start of a name or immediately following a slash mustbe matched explicitly, unless the shell option dotglob is set. When matching a pathname, the slashcharacter must always be matched explicitly. In other cases, the ``.'' character is not treated

bash_man_page of 63

specially. See the description of shopt below under SHELL BUILTIN COMMANDS for a description of thenocaseglob, nullglob, and dotglob shell options.

The GLOBIGNORE shell variable may be used to restrict the set of file names matching a pattern. IfGLOBIGNORE is set, each matching file name that also matches one of the patterns in GLOBIGNORE isremoved from the list of matches. The file names ``.'' and ``..'' are always ignored, even whenGLOBIGNORE is set. However, setting GLOBIGNORE has the effect of enabling the dotglob shell option,so all other file names beginning with a ``.'' will match. To get the old behavior of ignoring file namesbeginning with a ``.'', make ``.*'' one of the patterns in GLOBIGNORE. The dotglob option is disabledwhen GLOBIGNORE is unset.

Pattern Matching

Any character that appears in a pattern, other than the special pattern characters described below,matches itself. The NUL character may not occur in a pattern. The special pattern characters mustbe quoted if they are to be matched literally.

The special pattern characters have the following meanings:

*Matches any string, including the null string.

?Matches any single character.

[...]Matches any one of the enclosed characters. A pair of characters separated by a minus signdenotes a range; any character lexically between those two characters, inclusive, is matched.If the first character following the [ is a ! or a ^ then any character not enclosed is matched.A - may be matched by including it as the first or last character in the set. A ] may bematched by including it as the first character in the set.

Within [ and ], character classes can be specified using the syntax [:class:], where class is oneof the following classes defined in the POSIX.2 standard:

alnum alpha ascii blank cntrl digit graph lower print punct space upper xdigitA character class matches any character belonging to that class.

Within [ and ], an equivalence class can be specified using the syntax [=c=], which matchesall characters with the same collation weight (as defined by the current locale) as thecharacter c.

Within [ and ], the syntax [.symbol.] matches the collating symbol symbol.

If the extglob shell option is enabled using the shopt builtin, several extended pattern matchingoperators are recognized. In the following description, a pattern-list is a list of one or more patternsseparated by a |. Composite patterns may be formed using one or more of the following sub-patterns:

?(pattern-list)Matches zero or one occurrence of the given patterns*(pattern-list)Matches zero or more occurrences of the given patterns+(pattern-list)Matches one or more occurrences of the given patterns@(pattern-list)Matches exactly one of the given patterns!(pattern-list)

bash_man_page of 63

Matches anything except one of the given patterns

Quote Removal

After the preceding expansions, all unquoted occurrences of the characters \, ', and " that did notresult from one of the above expansions are removed.

REDIRECTIONBefore a command is executed, its input and output may be redirected using a special notationinterpreted by the shell. Redirection may also be used to open and close files for the current shellexecution environment. The following redirection operators may precede or appear anywhere withina simple command or may follow a command. Redirections are processed in the order they appear,from left to right.

In the following descriptions, if the file descriptor number is omitted, and the first character of theredirection operator is <, the redirection refers to the standard input (file descriptor 0). If the firstcharacter of the redirection operator is >, the redirection refers to the standard output (file descriptor1).

The word following the redirection operator in the following descriptions, unless otherwise noted, issubjected to brace expansion, tilde expansion, parameter expansion, command substitution,arithmetic expansion, quote removal, and pathname expansion. If it expands to more than one word,bash reports an error.

Note that the order of redirections is significant. For example, the command

ls > dirlist 2>&1

directs both standard output and standard error to the file dirlist, while the command

ls 2>&1 > dirlist

directs only the standard output to file dirlist, because the standard error was duplicated asstandard output before the standard output was redirected to dirlist.

A failure to open or create a file causes the redirection to fail.

Redirecting Input

Redirection of input causes the file whose name results from the expansion of word to be opened forreading on file descriptor n, or the standard input (file descriptor 0) if n is not specified.

The general format for redirecting input is:

[n]<word

Redirecting Output

bash_man_page of 63

Redirection of output causes the file whose name results from the expansion of word to be opened forwriting on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the filedoes not exist it is created; if it does exist it is truncated to zero size.

The general format for redirecting output is:

[n]>word

If the redirection operator is >, and the noclobber option to the set builtin has been enabled, theredirection will fail if the filename whose name results from the expansion of word exists and is aregular file. If the redirection operator is >|, or the redirection operator is > and the noclobberoption to the set builtin command is not enabled, the redirection is attempted even if the file namedby word exists.

Appending Redirected Output

Redirection of output in this fashion causes the file whose name results from the expansion of wordto be opened for appending on file descriptor n, or the standard output (file descriptor 1) if n is notspecified. If the file does not exist it is created.

The general format for appending output is:

[n]>>word

Redirecting Standard Output and Standard Error

Bash allows both the standard output (file descriptor 1) and the standard error output (filedescriptor 2) to be redirected to the file whose name is the expansion of word with this construct.

There are two formats for redirecting standard output and standard error:

&>word

and>&word

Of the two forms, the first is preferred. This is semantically equivalent to

>word 2>&1

Here Documents

This type of redirection instructs the shell to read input from the current source until a linecontaining only word (with no trailing blanks) is seen. All of the lines read up to that point are thenused as the standard input for a command.

The format of here-documents is as follows:

bash_man_page of 63

<<[-]word here-document delimiter

No parameter expansion, command substitution, pathname expansion, or arithmetic expansion isperformed on word. If any characters in word are quoted, the delimiter is the result of quote removalon word, and the lines in the here-document are not expanded. If word is unquoted, all lines of thehere-document are subjected to parameter expansion, command substitution, and arithmeticexpansion. In the latter case, the pair \<newline> is ignored, and \ must be used to quote thecharacters \, $, and `.

If the redirection operator is <<-, then all leading tab characters are stripped from input lines andthe line containing delimiter. This allows here-documents within shell scripts to be indented in anatural fashion.

Duplicating File Descriptors

The redirection operator

[n]<&word

is used to duplicate input file descriptors. If word expands to one or more digits, the file descriptordenoted by n is made to be a copy of that file descriptor. If the digits in word do not specify a filedescriptor open for input, a redirection error occurs. If word evaluates to -, file descriptor n is closed.If n is not specified, the standard input (file descriptor 0) is used.

The operator

[n]>&word

is used similarly to duplicate output file descriptors. If n is not specified, the standard output (filedescriptor 1) is used. If the digits in word do not specify a file descriptor open for output, aredirection error occurs. As a special case, if n is omitted, and word does not expand to one or moredigits, the standard output and standard error are redirected as described previously.

Opening File Descriptors for Reading and Writing

The redirection operator

[n]<>word

causes the file whose name is the expansion of word to be opened for both reading and writing on filedescriptor n, or on file descriptor 0 if n is not specified. If the file does not exist, it is created.

ALIASESAliases allow a string to be substituted for a word when it is used as the first word of a simplecommand. The shell maintains a list of aliases that may be set and unset with the alias and unaliasbuiltin commands (see SHELL BUILTIN COMMANDS below). The first word of each command, ifunquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. Thealias name and the replacement text may contain any valid shell input, including the metacharacterslisted above, with the exception that the alias name may not contain =. The first word of thereplacement text is tested for aliases, but a word that is identical to an alias being expanded is notexpanded a second time. This means that one may alias ls to ls -F, for instance, and bash does not

bash_man_page of 63

try to recursively expand the replacement text. If the last character of the alias value is a blank, thenthe next command word following the alias is also checked for alias expansion.

Aliases are created and listed with the alias command, and removed with the unalias command.

There is no mechanism for using arguments in the replacement text. If arguments are needed, ashell function should be used.

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell optionis set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS below).

The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads atleast one complete line of input before executing any of the commands on that line. Aliases areexpanded when a command is read, not when it is executed. Therefore, an alias definition appearingon the same line as another command does not take effect until the next line of input is read. Thecommands following the alias definition on that line are not affected by the new alias. This behavioris also an issue when functions are executed. Aliases are expanded when a function definition isread, not when the function is executed, because a function definition is itself a compound command.As a consequence, aliases defined in a function are not available until after that function is executed.To be safe, always put alias definitions on a separate line, and do not use alias in compoundcommands.

For almost every purpose, aliases are superseded by shell functions.

FUNCTIONSA shell function, defined as described above under SHELLGRAMMAR, stores a series of commands forlater execution. Functions are executed in the context of the current shell; no new process is createdto interpret them (contrast this with the execution of a shell script). When a function is executed, thearguments to the function become the positional parameters during its execution. The specialparameter # is updated to reflect the change. Positional parameter 0 is unchanged. All other aspectsof the shell execution environment are identical between a function and its caller with the exceptionthat the DEBUG trap (see the description of the trap builtin under SHELL BUILTIN COMMANDS below) isnot inherited.

Variables local to the function may be declared with the local builtin command. Ordinarily,variables and their values are shared between the function and its caller.

If the builtin command return is executed in a function, the function completes and executionresumes with the next command after the function call. When a function completes, the values of thepositional parameters and the special parameter # are restored to the values they had prior to thefunction's execution.

Function names and definitions may be listed with the -f option to the declare or typeset builtincommands. The -F option to declare or typeset will list the function names only. Functions may beexported so that subshells automatically have them defined with the -f option to the export builtin.

Functions may be recursive. No limit is imposed on the number of recursive calls.

ARITHMETIC EVALUATIONThe shell allows arithmetic expressions to be evaluated, under certain circumstances (see the letbuiltin command and Arithmetic Expansion). Evaluation is done in long integers with no check for

bash_man_page of 63

overflow, though division by 0 is trapped and flagged as an error. The following list of operators isgrouped into levels of equal-precedence operators. The levels are listed in order of decreasingprecedence.- +

unary minus and plus! ~

logical and bitwise negation**

exponentiation* / %

multiplication, division, remainder+ -

addition, subtraction<< >>

left and right bitwise shifts<= >= < >

comparison== !=

equality and inequality&

bitwise AND^

bitwise exclusive OR|

bitwise OR&&

logical AND||

logical ORexpr?expr:expr

conditional evaluation= *= /= %= += -= <<= >>= &= ^= |=

assignment

Shell variables are allowed as operands; parameter expansion is performed before the expression isevaluated. The value of a parameter is coerced to a long integer within an expression. A shellvariable need not have its integer attribute turned on to be used in an expression.

Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denoteshexadecimal. Otherwise, numbers take the form [base#]n, where base is a decimal number between 2and 64 representing the arithmetic base, and n is a number in that base. If base is omitted, thenbase 10 is used. The digits greater than 9 are represented by the lowercase letters, the uppercaseletters, _, and @, in that order. If base is less than or equal to 36, lowercase and uppercase lettersmay be used interchangably to represent numbers between 10 and 35.

Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated firstand may override the precedence rules above.

CONDITIONAL EXPRESSIONSConditional expressions are used by the [[ compound command and the test and [ builtin commandsto test file attributes and perform string and arithmetic comparisons. Expressions are formed fromthe following unary or binary primaries. If any file argument to one of the primaries is of the form/dev/fd/n, then file descriptor n is checked.-a file

True if file exists.

bash_man_page of 63

-b fileTrue if file exists and is a block special file.

-c fileTrue if file exists and is a character special file.

-d fileTrue if file exists and is a directory.

-e fileTrue if file exists.

-f fileTrue if file exists and is a regular file.

-g fileTrue if file exists and is set-group-id.

-k fileTrue if file exists and its ``sticky'' bit is set.

-p fileTrue if file exists and is a named pipe (FIFO).

-r fileTrue if file exists and is readable.

-s fileTrue if file exists and has a size greater than zero.

-t fdTrue if file descriptor fd is open and refers to a terminal.

-u fileTrue if file exists and its set-user-id bit is set.

-w fileTrue if file exists and is writable.

-x fileTrue if file exists and is executable.

-O fileTrue if file exists and is owned by the effective user id.

-G fileTrue if file exists and is owned by the effective group id.

-L fileTrue if file exists and is a symbolic link.

-S fileTrue if file exists and is a socket.

-N fileTrue if file exists and has been modified since it was last read.

file1 -nt file2True if file1 is newer (according to modification date) than file2.

file1 -ot file2True if file1 is older than file2.

file1 -ef file2True if file1 and file2 have the same device and inode numbers.

-o optnameTrue if shell option optname is enabled. See the list of options under the description of the -ooption to the set builtin below.

-z stringTrue if the length of string is zero.

-n stringstring

True if the length of string is non-zero.string1 == string2

True if the strings are equal. = may be used in place of ==.string1 != string2

True if the strings are not equal.string1 < string2

True if string1 sorts before string2 lexicographically in the current locale.

bash_man_page of 63

string1 > string2True if string1 sorts after string2 lexicographically in the current locale.

arg1 OP arg2OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1is equal to, not equal to, less than, less than or equal to, greater than, or greater than orequal to arg2, respectively. Arg1 and arg2 may be positive or negative integers.

SIMPLE COMMAND EXPANSIONWhen a simple command is executed, the shell performs the following expansions, assignments, andredirections, from left to right.1.

The words that the parser has marked as variable assignments (those preceding thecommand name) and redirections are saved for later processing.

2.The words that are not variable assignments or redirections are expanded. If any wordsremain after expansion, the first word is taken to be the name of the command and theremaining words are the arguments.

3.Redirections are performed as described above under REDIRECTION.

4.The text after the = in each variable assignment undergoes tilde expansion, parameterexpansion, command substitution, arithmetic expansion, and quote removal before beingassigned to the variable.

If no command name results, the variable assignments affect the current shell environment.Otherwise, the variables are added to the environment of the executed command and do not affectthe current shell environment. If any of the assignments attempts to assign a value to a readonlyvariable, an error occurs, and the command exits with a non-zero status.

If no command name results, redirections are performed, but do not affect the current shellenvironment. A redirection error causes the command to exit with a non-zero status.

If there is a command name left after expansion, execution proceeds as described below. Otherwise,the command exits. If one of the expansions contained a command substitution, the exit status of thecommand is the exit status of the last command substitution performed. If there were no commandsubstitutions, the command exits with a status of zero.

COMMAND EXECUTIONAfter a command has been split into words, if it results in a simple command and an optional list ofarguments, the following actions are taken.

If the command name contains no slashes, the shell attempts to locate it. If there exists a shellfunction by that name, that function is invoked as described above in FUNCTIONS. If the name doesnot match a function, the shell searches for it in the list of shell builtins. If a match is found, thatbuiltin is invoked.

If the name is neither a shell function nor a builtin, and contains no slashes, bash searches eachelement of the PATH for a directory containing an executable file by that name. Bash uses a hashtable to remember the full file names of executable files (see hash under SHELL BUILTIN COMMANDSbelow). A full search of the directories in PATH is performed only if the command is not found in the

bash_man_page of 63

hash table. If the search is unsuccessful, the shell prints an error message and returns an exit statusof 127.

If the search is successful, or if the command name contains one or more slashes, the shell executesthe named program in a separate execution environment. Argument 0 is set to the name given, andthe remaining arguments to the command are set to the arguments given, if any.

If this execution fails because the file is not in executable format, and the file is not a directory, it isassumed to be a shell script, a file containing shell commands. A subshell is spawned to execute it.This subshell reinitializes itself, so that the effect is as if a new shell had been invoked to handle thescript, with the exception that the locations of commands remembered by the parent (see hash belowunder SHELL BUILTIN COMMANDS) are retained by the child.

If the program is a file beginning with #!, the remainder of the first line specifies an interpreter forthe program. The shell executes the specified interpreter on operating systems that do not handlethis executable format themselves. The arguments to the interpreter consist of a single optionalargument following the interpreter name on the first line of the program, followed by the name of theprogram, followed by the command arguments, if any.

COMMAND EXECUTION ENVIRONMENTThe shell has an execution environment, which consists of the following:*

open files inherited by the shell at invocation, as modified by redirections supplied to theexec builtin

*the current working directory as set by cd, pushd, or popd, or inherited by the shell atinvocation

*the file creation mode mask as set by umask or inherited from the shell's parent

*current traps set by trap

*shell parameters that are set by variable assignment or with set or inherited from the shell'sparent in the environment

*shell functions defined during execution or inherited from the shell's parent in theenvironment

*options enabled at invocation (either by default or with command-line arguments) or by set

*options enabled by shopt

*shell aliases defined with alias

*various process IDs, including those of background jobs, the value of $$, and the value of$PPID

When a simple command other than a builtin or shell function is to be executed, it is invoked in aseparate execution environment that consists of the following. Unless otherwise noted, the valuesare inherited from the shell.

*the shell's open files, plus any modifications and additions specified by redirections to thecommand

*

bash_man_page of 63

the current working directory*

the file creation mode mask*

shell variables marked for export, along with variables exported for the command, passed inthe environment

*traps caught by the shell are reset to the values the inherited from the shell's parent, andtraps ignored by the shell are ignored

A command invoked in this separate environment cannot affect the shell's execution environment.

Command substitution and asynchronous commands are invoked in a subshell environment that is aduplicate of the shell environment, except that traps caught by the shell are reset to the values thatthe shell inherited from its parent at invocation. Builtin commands that are invoked as part of apipeline are also executed in a subshell environment. Changes made to the subshell environmentcannot affect the shell's execution environment.

ENVIRONMENTWhen a program is invoked it is given an array of strings called the environment. This is a list ofname-value pairs, of the form name=value.

The shell allows you to manipulate the environment in several ways. On invocation, the shell scansits own environment and creates a parameter for each name found, automatically marking it forexport to child processes. Executed commands inherit the environment. The export and declare -xcommands allow parameters and functions to be added to and deleted from the environment. If thevalue of a parameter in the environment is modified, the new value becomes part of theenvironment, replacing the old. The environment inherited by any executed command consists of theshell's initial environment, whose values may be modified in the shell, less any pairs removed by theunset command, plus any additions via the export and declare -x commands.

The environment for any simple command or function may be augmented temporarily by prefixing itwith parameter assignments, as described above in PARAMETERS. These assignment statementsaffect only the environment seen by that command.

If the -k option is set (see the set builtin command below), then all parameter assignments areplaced in the environment for a command, not just those that precede the command name.

When bash invokes an external command, the variable _ is set to the full file name of the commandand passed to that command in its environment.

EXIT STATUSFor the shell's purposes, a command which exits with a zero exit status has succeeded. An exit statusof zero indicates success. A non-zero exit status indicates failure. When a command terminates on afatal signal, bash uses the value of 128+signal as the exit status.

If a command is not found, the child process created to execute it returns a status of 127. If acommand is found but is not executable, the return status is 126.

If a command fails because of an error during expansion or redirection, the exit status is greaterthan zero.

bash_man_page of 63

Shell builtin commands return a status of 0 (true) if successful, and non-zero (false) if an error occurswhile they execute. All builtins return an exit status of 2 to indicate incorrect usage.

Bash itself returns the exit status of the last command executed, unless a syntax error occurs, inwhich case it exits with a non-zero value. See also the exit builtin command below.

SIGNALSWhen bash is interactive, in the absence of any traps, it ignores SIGTERM (so that kill 0 does not killan interactive shell), and SIGINT is caught and handled (so that the wait builtin is interruptible). Inall cases, bash ignores SIGQUIT. If job control is in effect, bash ignores SIGTTIN, SIGTTOU, and SIGTSTP.

Synchronous jobs started by bash have signal handlers set to the values inherited by the shell fromits parent. When job control is not in effect, asynchronous commands ignore SIGINT and SIGQUIT aswell. Commands run as a result of command substitution ignore the keyboard-generated job controlsignals SIGTTIN, SIGTTOU, and SIGTSTP.

The shell exits by default upon receipt of a SIGHUP. Before exiting, it resends the SIGHUP to all jobs,running or stopped. Stopped jobs are sent SIGCONT to ensure that they receive the SIGHUP. To preventthe shell from sending the signal to a particular job, it should be removed from the jobs table withthe disown builtin (see SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP usingdisown -h.

If the huponexit shell option has been set with shopt, bash sends a SIGHUP to all jobs when aninteractive login shell exits.

When bash receives a signal for which a trap has been set while waiting for a command to complete,the trap will not be executed until the command completes. When bash is waiting for anasynchronous command via the wait builtin, the reception of a signal for which a trap has been setwill cause the wait builtin to return immediately with an exit status greater than 128, immediatelyafter which the trap is executed.

JOB CONTROLJob control refers to the ability to selectively stop (suspend) the execution of processes and continue(resume) their execution at a later point. A user typically employs this facility via an interactiveinterface supplied jointly by the system's terminal driver and bash.

The shell associates a job with each pipeline. It keeps a table of currently executing jobs, which maybe listed with the jobs command. When bash starts a job asynchronously (in the background), itprints a line that looks like:

[1] 25647

indicating that this job is job number 1 and that the process ID of the last process in the pipelineassociated with this job is 25647. All of the processes in a single pipeline are members of the samejob. Bash uses the job abstraction as the basis for job control.

To facilitate the implementation of the user interface to job control, the system maintains the notionof a current terminal process group ID. Members of this process group (processes whose processgroup ID is equal to the current terminal process group ID) receive keyboard-generated signals suchas SIGINT. These processes are said to be in the foreground. Background processes are those whoseprocess group ID differs from the terminal's; such processes are immune to keyboard-generated

bash_man_page of 63

signals. Only foreground processes are allowed to read from or write to the terminal. Backgroundprocesses which attempt to read from (write to) the terminal are sent a SIGTTIN (SIGTTOU) signal bythe terminal driver, which, unless caught, suspends the process.

If the operating system on which bash is running supports job control, bash allows you to use it.Typing the suspend character (typically ^Z, Control-Z) while a process is running causes that processto be stopped and returns you to bash. Typing the delayed suspend character (typically ^Y, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control tobe returned to bash. The user may then manipulate the state of this job, using the bg command tocontinue it in the background, the fg command to continue it in the foreground, or the kill commandto kill it. A ^Z takes effect immediately, and has the additional side effect of causing pending outputand typeahead to be discarded.

There are a number of ways to refer to a job in the shell. The character % introduces a job name. Jobnumber n may be referred to as %n. A job may also be referred to using a prefix of the name used tostart it, or using a substring that appears in its command line. For example, %ce refers to a stoppedce job. If a prefix matches more than one job, bash reports an error. Using %?ce, on the other hand,refers to any job containing the string ce in its command line. If the substring matches more thanone job, bash reports an error. The symbols %% and %+ refer to the shell's notion of the current job,which is the last job stopped while it was in the foreground or started in the background. Theprevious job may be referenced using %-. In output pertaining to jobs (e.g., the output of the jobscommand), the current job is always flagged with a +, and the previous job with a -.

Simply naming a job can be used to bring it into the foreground: %1 is a synonym for ``fg %1'',bringing job 1 from the background into the foreground. Similarly, ``%1 &'' resumes job 1 in thebackground, equivalent to ``bg %1''.

The shell learns immediately whenever a job changes state. Normally, bash waits until it is about toprint a prompt before reporting changes in a job's status so as to not interrupt any other output. Ifthe -b option to the set builtin command is enabled, bash reports such changes immediately.

If an attempt to exit bash is made while jobs are stopped, the shell prints a warning message. Thejobs command may then be used to inspect their status. If a second attempt to exit is made withoutan intervening command, the shell does not print another warning, and the stopped jobs areterminated.

PROMPTINGWhen executing interactively, bash displays the primary prompt PS1 when it is ready to read acommand, and the secondary prompt PS2 when it needs more input to complete a command. Bashallows these prompt strings to be customized by inserting a number of backslash-escaped specialcharacters that are decoded as follows:

\aan ASCII bell character (07)\dthe date in "Weekday Month Date" format (e.g., "Tue May 26")\ean ASCII escape character (033)\hthe hostname up to the first `.'\Hthe hostname\nnewline\rcarriage return

bash_man_page of 63

\sthe name of the shell, the basename of $0 (the portion following the final slash)\tthe current time in 24-hour HH:MM:SS format\Tthe current time in 12-hour HH:MM:SS format\@the current time in 12-hour am/pm format\uthe username of the current user\vthe version of bash (e.g., 2.00)\Vthe release of bash, version + patchlevel (e.g., 2.00.0)\wthe current working directory\Wthe basename of the current working directory\!the history number of this command\#the command number of this command\$if the effective UID is 0, a #, otherwise a $\nnnthe character corresponding to the octal number nnn\\a backslash\[begin a sequence of non-printing characters, which could be used to embed a terminal controlsequence into the prompt\]end a sequence of non-printing characters

The command number and the history number are usually different: the history number of acommand is its position in the history list, which may include commands restored from the historyfile (see HISTORY below), while the command number is the position in the sequence of commandsexecuted during the current shell session. After the string is decoded, it is expanded via parameterexpansion, command substitution, arithmetic expansion, string expansion, and quote removal,subject to the value of the promptvars shell option (see the description of the shopt commandunder SHELL BUILTIN COMMANDS below).

READLINEThis is the library that handles reading input when using an interactive shell, unless the --noediting option is given at shell invocation. By default, the line editing commands are similar tothose of emacs. A vi-style line editing interface is also available. To turn off line editing after theshell is running, use the +o emacs or +o vi options to the set builtin (see SHELL BUILTIN COMMANDSbelow).

Readline Notation

In this section, the emacs-style notation is used to denote keystrokes. Control keys are denoted by C-key, e.g., C-n means Control-N. Similarly, meta keys are denoted by M-key, so M-x means Meta-X.(On keyboards without a meta key, M-x means ESC x, i.e., press the Escape key then the x key. This

bash_man_page of 63

makes ESC the meta prefix. The combination M-C-x means ESC-Control-x, or press the Escape keythen hold the Control key while pressing the x key.)

Readline commands may be given numeric arguments, which normally act as a repeat count.Sometimes, however, it is the sign of the argument that is significant. Passing a negative argumentto a command that acts in the forward direction (e.g., kill-line) causes that command to act in abackward direction. Commands whose behavior with arguments deviates from this are noted below.

When a command is described as killing text, the text deleted is saved for possible future retrieval(yanking). The killed text is saved in a kill ring. Consecutive kills cause the text to be accumulatedinto one unit, which can be yanked all at once. Commands which do not kill text separate the chunksof text on the kill ring.

Readline Initialization

Readline is customized by putting commands in an initialization file (the inputrc file). The name ofthis file is taken from the value of the INPUTRC variable. If that variable is unset, the default is~/.inputrc. When a program which uses the readline library starts up, the initialization file is read,and the key bindings and variables are set. There are only a few basic constructs allowed in thereadline initialization file. Blank lines are ignored. Lines beginning with a # are comments. Linesbeginning with a $ indicate conditional constructs. Other lines denote key bindings and variablesettings.

The default key-bindings may be changed with an inputrc file. Other programs that use this librarymay add their own commands and bindings.

For example, placing

M-Control-u: universal-argument

orC-Meta-u: universal-argument

into the inputrc would make M-C-u execute the readline command universal-argument.

The following symbolic character names are recognized: RUBOUT, DEL, ESC, LFD, NEWLINE,RET, RETURN, SPC, SPACE, and TAB. In addition to command names, readline allows keys to bebound to a string that is inserted when the key is pressed (a macro).

Readline Key Bindings

The syntax for controlling key bindings in the inputrc file is simple. All that is required is the nameof the command or the text of a macro and a key sequence to which it should be bound. The namemay be specified in one of two ways: as a symbolic key name, possibly with Meta- or Control-prefixes, or as a key sequence. When using the form keyname:function-name or macro, keyname isthe name of a key spelled out in English. For example:

Control-u: universal-argumentMeta-Rubout: backward-kill-wordControl-o: "> output"

In the above example, C-u is bound to the function universal-argument, M-DEL is bound to thefunction backward-kill-word, and C-o is bound to run the macro expressed on the right hand side(that is, to insert the text > output into the line).

bash_man_page of 63

In the second form, "keyseq":function-name or macro, keyseq differs from keyname above in thatstrings denoting an entire key sequence may be specified by placing the sequence within doublequotes. Some GNU Emacs style key escapes can be used, as in the following example.

"\C-u": universal-argument"\C-x\C-r": re-read-init-file"\e[11~": "Function Key 1"

In this example, C-u is again bound to the function universal-argument. C-x C-r is bound to thefunction re-read-init-file, and ESC [ 1 1 ~ is bound to insert the text Function Key 1. The full setof GNU Emacs style escape sequences is

\C-control prefix\M-meta prefix\ean escape character\\backslash\literal "\'literal '

In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:

\aalert (bell)\bbackspace\ddelete\fform feed\nnewline\rcarriage return\thorizontal tab\vvertical tab\nnnthe character whose ASCII code is the octal value nnn (one to three digits)\xnnnthe character whose ASCII code is the hexadecimal value nnn (one to three digits)

When entering the text of a macro, single or double quotes must be used to indicate a macrodefinition. Unquoted text is assumed to be a function name. In the macro body, the backslashescapes described above are expanded. Backslash will quote any other character in the macro text,including " and '.

Bash allows the current readline key bindings to be displayed or modified with the bind builtincommand. The editing mode may be switched during interactive use by using the -o option to the setbuiltin command (see SHELL BUILTIN COMMANDS below).

bash_man_page of 63

Readline Variables

Readline has variables that can be used to further customize its behavior. A variable may be set inthe inputrc file with a statement of the form

set variable-name value

Except where noted, readline variables can take the values On or Off. The variables and theirdefault values are:

bell-style (audible)Controls what happens when readline wants to ring the terminal bell. If set to none,readline never rings the bell. If set to visible, readline uses a visible bell if one is available.If set to audible, readline attempts to ring the terminal's bell.

comment-begin (``#'')The string that is inserted when the readline insert-comment command is executed. Thiscommand is bound to M-# in emacs mode and to # in vi command mode.

completion-ignore-case (Off)If set to On, readline performs filename matching and completion in a case-insensitivefashion.

completion-query-items (100)This determines when the user is queried about viewing the number of possible completionsgenerated by the possible-completions command. It may be set to any integer valuegreater than or equal to zero. If the number of possible completions is greater than or equalto the value of this variable, the user is asked whether or not he wishes to view them;otherwise they are simply listed on the terminal.

convert-meta (On)If set to On, readline will convert characters with the eighth bit set to an ASCII keysequence by stripping the eighth bit and prepending an escape character (in effect, usingescape as the meta prefix).

disable-completion (Off)If set to On, readline will inhibit word completion. Completion characters will be insertedinto the line as if they had been mapped to self-insert.

editing-mode (emacs)Controls whether readline begins with a set of key bindings similar to emacs or vi. editing-mode can be set to either emacs or vi.

enable-keypad (Off)When set to On, readline will try to enable the application keypad when it is called. Somesystems need this to enable the arrow keys.

expand-tilde (Off)If set to on, tilde expansion is performed when readline attempts word completion.

horizontal-scroll-mode (Off)When set to On, makes readline use a single line for display, scrolling the input horizontallyon a single screen line when it becomes longer than the screen width rather than wrappingto a new line.

input-meta (Off)If set to On, readline will enable eight-bit input (that is, it will not strip the high bit from thecharacters it reads), regardless of what the terminal claims it can support. The name meta-flag is a synonym for this variable.

keymap (emacs)Set the current readline keymap. The set of valid keymap names is emacs, emacs-standard,emacs-meta, emacs-ctlx, vi, vi-command, and vi-insert. vi is equivalent to vi-command; emacsis equivalent to emacs-standard. The default value is emacs; the value of editing-mode alsoaffects the default keymap.

mark-directories (On)If set to On, completed directory names have a slash appended.

mark-modified-lines (Off)

bash_man_page of 63

If set to On, history lines that have been modified are displayed with a preceding asterisk(*).

output-meta (Off)If set to On, readline will display characters with the eighth bit set directly rather than as ameta-prefixed escape sequence.

print-completions-horizontally (Off)If set to On, readline will display completions with matches sorted horizontally inalphabetical order, rather than down the screen.

show-all-if-ambiguous (Off)This alters the default behavior of the completion functions. If set to on, words which havemore than one possible completion cause the matches to be listed immediately instead ofringing the bell.

visible-stats (Off)If set to On, a character denoting a file's type as reported by stat(2) is appended to thefilename when listing possible completions.

Readline Conditional Constructs

Readline implements a facility similar in spirit to the conditional compilation features of the Cpreprocessor which allows key bindings and variable settings to be performed as the result of tests.There are four parser directives used.

$ifThe $if construct allows bindings to be made based on the editing mode, the terminal beingused, or the application using readline. The text of the test extends to the end of the line; nocharacters are required to isolate it.modeThe mode= form of the $if directive is used to test whether readline is in emacs or vi mode.This may be used in conjunction with the set keymap command, for instance, to setbindings in the emacs-standard and emacs-ctlx keymaps only if readline is starting out inemacs mode.termThe term= form may be used to include terminal-specific key bindings, perhaps to bind thekey sequences output by the terminal's function keys. The word on the right side of the = istested against the both full name of the terminal and the portion of the terminal name beforethe first -. This allows sun to match both sun and sun-cmd, for instance.applicationThe application construct is used to include application-specific settings. Each programusing the readline library sets the application name, and an initialization file can test for aparticular value. This could be used to bind key sequences to functions useful for a specificprogram. For instance, the following command adds a key sequence that quotes the currentor previous word in Bash: $if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif

$endifThis command, as seen in the previous example, terminates an $if command.

$elseCommands in this branch of the $if directive are executed if the test fails.

$includeThis directive takes a single filename as an argument and reads commands and bindingsfrom that file. For example, the following directive would read /etc/inputrc: $include /etc/inputrc

Searching

bash_man_page of 63

Readline provides commands for searching through the command history (see HISTORY below) forlines containing a specified string. There are two search modes: incremental and non-incremental.

Incremental searches begin before the user has finished typing the search string. As each characterof the search string is typed, readline displays the next entry from the history matching the stringtyped so far. An incremental search requires only as many characters as needed to find the desiredhistory entry. The Escape character is used to terminate an incremental search. Control-J will alsoterminate the search. Control-G will abort an incremental search and restore the original line. Whenthe search is terminated, the history entry containing the search string becomes the current line. Tofind other matching entries in the history list, type Control-S or Control-R as appropriate. This willsearch backward or forward in the history for the next entry matching the search string typed so far.Any other key sequence bound to a readline command will terminate the search and execute thatcommand. For instance, a newline will terminate the search and accept the line, thereby executingthe command from the history list.

Non-incremental searches read the entire search string before starting to search for matchinghistory lines. The search string may be typed by the user or be part of the contents of the currentline.

Readline Command Names

The following is a list of the names of the commands and the default key sequences to which they arebound. Command names without an accompanying key sequence are unbound by default.

Commands for Moving

beginning-of-line (C-a)Move to the start of the current line.

end-of-line (C-e)Move to the end of the line.

forward-char (C-f)Move forward a character.

backward-char (C-b)Move back a character.

forward-word (M-f)Move forward to the end of the next word. Words are composed of alphanumeric characters(letters and digits).

backward-word (M-b)Move back to the start of this, or the previous, word. Words are composed of alphanumericcharacters (letters and digits).

clear-screen (C-l)Clear the screen leaving the current line at the top of the screen. With an argument, refreshthe current line without clearing the screen.

redraw-current-lineRefresh the current line.

Commands for Manipulating the History

accept-line (Newline, Return)Accept the line regardless of where the cursor is. If this line is non-empty, add it to thehistory list according to the state of the HISTCONTROL variable. If the line is a modifiedhistory line, then restore the history line to its original state.

previous-history (C-p)Fetch the previous command from the history list, moving back in the list.

bash_man_page of 63

next-history (C-n)Fetch the next command from the history list, moving forward in the list.

beginning-of-history (M-<)Move to the first line in the history.

end-of-history (M->)Move to the end of the input history, i.e., the line currently being entered.

reverse-search-history (C-r)Search backward starting at the current line and moving `up' through the history asnecessary. This is an incremental search.

forward-search-history (C-s)Search forward starting at the current line and moving `down' through the history asnecessary. This is an incremental search.

non-incremental-reverse-search-history (M-p)Search backward through the history starting at the current line using a non-incrementalsearch for a string supplied by the user.

non-incremental-forward-search-history (M-n)Search forward through the history using a non-incremental search for a string supplied bythe user.

history-search-forwardSearch forward through the history for the string of characters between the start of thecurrent line and the current cursor position (the point). This is a non-incremental search.

history-search-backwardSearch backward through the history for the string of characters between the start of thecurrent line and the point. This is a non-incremental search.

yank-nth-arg (M-C-y)Insert the first argument to the previous command (usually the second word on the previousline) at point (the current cursor position). With an argument n, insert the nth word from theprevious command (the words in the previous command begin with word 0). A negativeargument inserts the nth word from the end of the previous command.

yank-last-arg (M-., M-_)Insert the last argument to the previous command (the last word of the previous historyentry). With an argument, behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last argument of each line in turn.

shell-expand-line (M-C-e)Expand the line as the shell does. This performs alias and history expansion as well as all ofthe shell word expansions. See HISTORY EXPANSION below for a description of historyexpansion.

history-expand-line (M-^)Perform history expansion on the current line. See HISTORY EXPANSION below for adescription of history expansion.

magic-spacePerform history expansion on the current line and insert a space. See HISTORY EXPANSIONbelow for a description of history expansion.

alias-expand-linePerform alias expansion on the current line. See ALIASES above for a description of aliasexpansion.

history-and-alias-expand-linePerform history and alias expansion on the current line.

insert-last-argument (M-., M-_)A synonym for yank-last-arg.

operate-and-get-next (C-o)Accept the current line for execution and fetch the next line relative to the current line fromthe history for editing. Any argument is ignored.

Commands for Changing Text

delete-char (C-d)

bash_man_page of 63

Delete the character under the cursor. If point is at the beginning of the line, there are nocharacters in the line, and the last character typed was not bound to delete-char, thenreturn EOF.

backward-delete-char (Rubout)Delete the character behind the cursor. When given a numeric argument, save the deletedtext on the kill ring.

quoted-insert (C-q, C-v)Add the next character typed to the line verbatim. This is how to insert characters like C-q,for example.

tab-insert (C-v TAB)Insert a tab character.

self-insert (a, b, A, 1, !, ...)Insert the character typed.

transpose-chars (C-t)Drag the character before point forward over the character at point. Point moves forward aswell. If point is at the end of the line, then transpose the two characters before point.Negative arguments don't work.

transpose-words (M-t)Drag the word behind the cursor past the word in front of the cursor moving the cursor overthat word as well.

upcase-word (M-u)Uppercase the current (or following) word. With a negative argument, uppercase theprevious word, but do not move point.

downcase-word (M-l)Lowercase the current (or following) word. With a negative argument, lowercase the previousword, but do not move point.

capitalize-word (M-c)Capitalize the current (or following) word. With a negative argument, capitalize the previousword, but do not move point.

Killing and Yanking

kill-line (C-k)Kill the text from the current cursor position to the end of the line.

backward-kill-line (C-x Rubout)Kill backward to the beginning of the line.

unix-line-discard (C-u)Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring.

kill-whole-lineKill all characters on the current line, no matter where the cursor is.

kill-word (M-d)Kill from the cursor to the end of the current word, or if between words, to the end of the nextword. Word boundaries are the same as those used by forward-word.

backward-kill-word (M-Rubout)Kill the word behind the cursor. Word boundaries are the same as those used by backward-word.

unix-word-rubout (C-w)Kill the word behind the cursor, using white space as a word boundary. The word boundariesare different from backward-kill-word.

delete-horizontal-space (M-\)Delete all spaces and tabs around point.

kill-regionKill the text between the point and mark (saved cursor position). This text is referred to asthe region.

copy-region-as-killCopy the text in the region to the kill buffer.

copy-backward-word

bash_man_page of 63

Copy the word before point to the kill buffer. The word boundaries are the same asbackward-word.

copy-forward-wordCopy the word following point to the kill buffer. The word boundaries are the same asforward-word.

yank (C-y)Yank the top of the kill ring into the buffer at the cursor.

yank-pop (M-y)Rotate the kill ring, and yank the new top. Only works following yank or yank-pop.

Numeric Arguments

digit-argument (M-0, M-1, ..., M--)Add this digit to the argument already accumulating, or start a new argument. M-- starts anegative argument.

universal-argumentThis is another way to specify an argument. If this command is followed by one or moredigits, optionally with a leading minus sign, those digits define the argument. If thecommand is followed by digits, executing universal-argument again ends the numericargument, but is otherwise ignored. As a special case, if this command is immediatelyfollowed by a character that is neither a digit or minus sign, the argument count for the nextcommand is multiplied by four. The argument count is initially one, so executing thisfunction the first time makes the argument count four, a second time makes the argumentcount sixteen, and so on.

Completing

complete (TAB)Attempt to perform completion on the text before point. Bash attempts completion treatingthe text as a variable (if the text begins with $), username (if the text begins with ~),hostname (if the text begins with @), or command (including aliases and functions) in turn. Ifnone of these produces a match, filename completion is attempted.

possible-completions (M-?)List the possible completions of the text before point.

insert-completions (M-*)Insert all completions of the text before point that would have been generated by possible-completions.

menu-completeSimilar to complete, but replaces the word to be completed with a single match from the listof possible completions. Repeated execution of menu-complete steps through the list ofpossible completions, inserting each match in turn. At the end of the list of completions, thebell is rung and the original text is restored. An argument of n moves n positions forward inthe list of matches; a negative argument may be used to move backward through the list.This command is intended to be bound to TAB, but is unbound by default.

complete-filename (M-/)Attempt filename completion on the text before point.

possible-filename-completions (C-x /)List the possible completions of the text before point, treating it as a filename.

complete-username (M-~)Attempt completion on the text before point, treating it as a username.

possible-username-completions (C-x ~)List the possible completions of the text before point, treating it as a username.

complete-variable (M-$)Attempt completion on the text before point, treating it as a shell variable.

possible-variable-completions (C-x $)

bash_man_page of 63

List the possible completions of the text before point, treating it as a shell variable.complete-hostname (M-@)

Attempt completion on the text before point, treating it as a hostname.possible-hostname-completions (C-x @)

List the possible completions of the text before point, treating it as a hostname.complete-command (M-!)

Attempt completion on the text before point, treating it as a command name. Commandcompletion attempts to match the text against aliases, reserved words, shell functions, shellbuiltins, and finally executable filenames, in that order.

possible-command-completions (C-x !)List the possible completions of the text before point, treating it as a command name.

dynamic-complete-history (M-TAB)Attempt completion on the text before point, comparing the text against lines from thehistory list for possible completion matches.

complete-into-braces (M-{)Perform filename completion and return the list of possible completions enclosed withinbraces so the list is available to the shell (see Brace Expansion above).

Keyboard Macros

start-kbd-macro (C-x ()Begin saving the characters typed into the current keyboard macro.

end-kbd-macro (C-x ))Stop saving the characters typed into the current keyboard macro and store the definition.

call-last-kbd-macro (C-x e)Re-execute the last keyboard macro defined, by making the characters in the macro appearas if typed at the keyboard.

Miscellaneous

re-read-init-file (C-x C-r)Read in the contents of the inputrc file, and incorporate any bindings or variableassignments found there.

abort (C-g)Abort the current editing command and ring the terminal's bell (subject to the setting ofbell-style).

do-uppercase-version (M-a, M-b, M-x, ...)If the metafied character x is lowercase, run the command that is bound to the correspondinguppercase character.

prefix-meta (ESC)Metafy the next character typed. ESC f is equivalent to Meta-f.

undo (C-_, C-x C-u)Incremental undo, separately remembered for each line.

revert-line (M-r)Undo all changes made to this line. This is like executing the undo command enough timesto return the line to its initial state.

tilde-expand (M-~)Perform tilde expansion on the current word.

set-mark (C-@, M-<space>)Set the mark to the current point. If a numeric argument is supplied, the mark is set to thatposition.

exchange-point-and-mark (C-x C-x)Swap the point with the mark. The current cursor position is set to the saved position, andthe old cursor position is saved as the mark.

character-search (C-])

bash_man_page of 63

A character is read and point is moved to the next occurrence of that character. A negativecount searches for previous occurrences.

character-search-backward (M-C-])A character is read and point is moved to the previous occurrence of that character. Anegative count searches for subsequent occurrences.

insert-comment (M-#)The value of the readline comment-begin variable is inserted at the beginning of thecurrent line, and the line is accepted as if a newline had been typed. This makes the currentline a shell comment.

glob-expand-word (C-x *)The word before point is treated as a pattern for pathname expansion, and the list ofmatching file names is inserted, replacing the word.

glob-list-expansions (C-x g)The list of expansions that would have been generated by glob-expand-word is displayed,and the line is redrawn.

dump-functionsPrint all of the functions and their key bindings to the readline output stream. If a numericargument is supplied, the output is formatted in such a way that it can be made part of aninputrc file.

dump-variablesPrint all of the settable readline variables and their values to the readline output stream. If anumeric argument is supplied, the output is formatted in such a way that it can be madepart of an inputrc file.

dump-macrosPrint all of the readline key sequences bound to macros and the strings they ouput. If anumeric argument is supplied, the output is formatted in such a way that it can be madepart of an inputrc file.

display-shell-version (C-x C-v)Display version information about the current instance of bash.

HISTORYWhen the -o history option to the set builtin is enabled, the shell provides access to the commandhistory, the list of commands previously typed. The text of the last HISTSIZE commands (default 500)is saved in a history list. The shell stores each command in the history list prior to parameter andvariable expansion (see EXPANSION above) but after history expansion is performed, subject to thevalues of the shell variables HISTIGNORE and HISTCONTROL. On startup, the history is initialized fromthe file named by the variable HISTFILE (default ~/.bash_history). HISTFILE is truncated, if necessary,to contain no more than HISTFILESIZE lines. When an interactive shell exits, the last HISTSIZE linesare copied from the history list to HISTFILE. If the histappend shell option is enabled (see thedescription of shopt under SHELL BUILTIN COMMANDS below), the lines are appended to the historyfile, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file is unwritable,the history is not saved. After saving the history, the history file is truncated to contain no morethan HISTFILESIZE lines. If HISTFILESIZE is not set, no truncation is performed.

The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit and re-execute a portion of the history list. The history builtin can be used to display or modify the historylist and manipulate the history file. When using the command-line editing, search commands areavailable in each editing mode that provide access to the history list.

The shell allows control over which commands are saved on the history list. The HISTCONTROL andHISTIGNORE variables may be set to cause the shell to save only a subset of the commands entered.The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-linecommand in the same history entry, adding semicolons where necessary to preserve syntacticcorrectness. The lithist shell option causes the shell to save the command with embedded newlines

bash_man_page of 63

instead of semicolons. See the description of the shopt builtin below under SHELL BUILTIN COMMANDSfor information on setting and unsetting shell options.

HISTORY EXPANSIONThe shell supports a history expansion feature that is similar to the history expansion in csh. Thissection describes what syntax features are available. This feature is enabled by default forinteractive shells, and can be disabled using the +H option to the set builtin command (see SHELLBUILTIN COMMANDS below). Non-interactive shells do not perform history expansion by default.

History expansions introduce words from the history list into the input stream, making it easy torepeat commands, insert the arguments to a previous command into the current input line, or fixerrors in previous commands quickly.

History expansion is performed immediately after a complete line is read, before the shell breaks itinto words. It takes place in two parts. The first is to determine which line from the history list touse during substitution. The second is to select portions of that line for inclusion into the currentone. The line selected from the history is the event, and the portions of that line that are acted uponare words. Various modifiers are available to manipulate the selected words. The line is broken intowords in the same fashion as when reading input, so that several metacharacter-separated wordssurrounded by quotes are considered one word. History expansions are introduced by the appearanceof the history expansion character, which is ! by default. Only backslash (\) and single quotes canquote the history expansion character.

Several shell options settable with the shopt builtin may be used to tailor the behavior of historyexpansion. If the histverify shell option is enabled (see the description of the shopt builtin), andreadline is being used, history substitutions are not immediately passed to the shell parser.Instead, the expanded line is reloaded into the readline editing buffer for further modification. Ifreadline is being used, and the histreedit shell option is enabled, a failed history substitution willbe reloaded into the readline editing buffer for correction. The -p option to the history builtincommand may be used to see what a history expansion will do before using it. The -s option to thehistory builtin may be used to add commands to the end of the history list without actuallyexecuting them, so that they are available for subsequent recall.

The shell allows control of the various characters used by the history expansion mechanism (see thedescription of histchars above under Shell Variables).

Event Designators

An event designator is a reference to a command line entry in the history list.

!Start a history substitution, except when followed by a blank, newline, = or (.

!nRefer to command line n.

!-nRefer to the current command line minus n.

!!Refer to the previous command. This is a synonym for `!-1'.

!stringRefer to the most recent command starting with string.

!?string[?]Refer to the most recent command containing string. The trailing ? may be omitted if stringis followed immediately by a newline.

bash_man_page of 63

^string1^string2^Quick substitution. Repeat the last command, replacing string1 with string2. Equivalent to``!!:s/string1/string2/'' (see Modifiers below).

!#The entire command line typed so far.

Word Designators

Word designators are used to select desired words from the event. A : separates the eventspecification from the word designator. It may be omitted if the word designator begins with a ^, $, *,-, or %. Words are numbered from the beginning of the line, with the first word being denoted by 0(zero). Words are inserted into the current line separated by single spaces.

0 (zero)The zeroth word. For the shell, this is the command word.

nThe nth word.

^The first argument. That is, word 1.

$The last argument.

%The word matched by the most recent `?string?' search.

x-yA range of words; `-y' abbreviates `0-y'.

*All of the words but the zeroth. This is a synonym for `1-$'. It is not an error to use * if thereis just one word in the event; the empty string is returned in that case.

x*Abbreviates x-$.

x-Abbreviates x-$ like x*, but omits the last word.

If a word designator is supplied without an event specification, the previous command is used as theevent.

Modifiers

After the optional word designator, there may appear a sequence of one or more of the followingmodifiers, each preceded by a `:'.

hRemove a trailing file name component, leaving only the head.

tRemove all leading file name components, leaving the tail.

rRemove a trailing suffix of the form .xxx, leaving the basename.

eRemove all but the trailing suffix.

pPrint the new command but do not execute it.

qQuote the substituted words, escaping further substitutions.

x

bash_man_page of 63

Quote the substituted words as with q, but break into words at blanks and newlines.s/old/new/

Substitute new for the first occurrence of old in the event line. Any delimiter can be used inplace of /. The final delimiter is optional if it is the last character of the event line. Thedelimiter may be quoted in old and new with a single backslash. If & appears in new, it isreplaced by old. A single backslash will quote the &. If old is null, it is set to the last oldsubstituted, or, if no previous history substitutions took place, the last string in a !?string[?]search.

&Repeat the previous substitution.

gCause changes to be applied over the entire event line. This is used in conjunction with `:s'(e.g., `:gs/old/new/') or `:&'. If used with `:s', any delimiter can be used in place of /, and thefinal delimiter is optional if it is the last character of the event line.

SHELL BUILTIN COMMANDSUnless otherwise noted, each builtin command documented in this section as accepting optionspreceded by - accepts -- to signify the end of the options.

: [arguments]No effect; the command does nothing beyond expanding arguments and performing anyspecified redirections. A zero exit code is returned.. filename [arguments]

source filename [arguments]Read and execute commands from filename in the current shell environment and return theexit status of the last command executed from filename. If filename does not contain a slash,file names in PATH are used to find the directory containing filename. The file searched for inPATH need not be executable. The current directory is searched if no file is found in PATH. Ifthe sourcepath option to the shopt builtin command is turned off, the PATH is not searched.If any arguments are supplied, they become the positional parameters when filename isexecuted. Otherwise the positional parameters are unchanged. The return status is thestatus of the last command exited within the script (0 if no commands are executed), andfalse if filename is not found or cannot be read.

alias [-p] [name[=value] ...]Alias with no arguments or with the -p option prints the list of aliases in the form aliasname=value on standard output. When arguments are supplied, an alias is defined for eachname whose value is given. A trailing space in value causes the next word to be checked foralias substitution when the alias is expanded. For each name in the argument list for whichno value is supplied, the name and value of the alias is printed. Alias returns true unless aname is given for which no alias has been defined.

bg [jobspec]Resume the suspended job jobspec in the background, as if it had been started with &. Ifjobspec is not present, the shell's notion of the current job is used. bg jobspec returns 0 unlessrun when job control is disabled or, when run with job control enabled, if jobspec was notfound or started without job control.bind [-m keymap] [-lpsvPSV]

bind [-m keymap] [-q function] [-u function] [-r keyseq]bind [-m keymap] -f filenamebind [-m keymap] keyseq:function-name

Display current readline key and function bindings, or bind a key sequence to a readlinefunction or macro. The binding syntax accepted is identical to that of .inputrc, but eachbinding must be passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Options,if supplied, have the following meanings:-m keymap

bash_man_page of 63

Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymapnames are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-command, and vi-insert. viis equivalent to vi-command; emacs is equivalent to emacs-standard.-lList the names of all readline functions.-pDisplay readline function names and bindings in such a way that they can be re-read.-PList current readline function names and bindings.-vDisplay readline variable names and values in such a way that they can be re-read.-VList current readline variable names and values.-sDisplay readline key sequences bound to macros and the strings they output in such a waythat they can be re-read.-SDisplay readline key sequences bound to macros and the strings they output.-f filenameRead key bindings from filename.-q functionQuery about which keys invoke the named function.-u functionUnbind all keys bound to the named function.-r keyseqRemove any current binding for keyseq.

The return value is 0 unless an unrecognized option is given or an error occurred.

break [n]Exit from within a for, while, until, or select loop. If n is specified, break n levels. n mustbe >= 1. If n is greater than the number of enclosing loops, all enclosing loops are exited. Thereturn value is 0 unless the shell is not executing a loop when break is executed.

builtin shell-builtin [arguments]Execute the specified shell builtin, passing it arguments, and return its exit status. This isuseful when defining a function whose name is the same as a shell builtin, retaining thefunctionality of the builtin within the function. The cd builtin is commonly redefined thisway. The return status is false if shell-builtin is not a shell builtin command.

cd [-LP] [dir]Change the current directory to dir. The variable HOME is the default dir. The variableCDPATH defines the search path for the directory containing dir. Alternative directory namesin CDPATH are separated by a colon (:). A null directory name in CDPATH is the same as thecurrent directory, i.e., ``.''. If dir begins with a slash (/), then CDPATH is not used. The -Poption says to use the physical directory structure instead of following symbolic links (seealso the -P option to the set builtin command); the -L option forces symbolic links to befollowed. An argument of - is equivalent to $OLDPWD. The return value is true if the directorywas successfully changed; false otherwise.

command [-pVv] command [arg ...]Run command with args suppressing the normal shell function lookup. Only builtincommands or commands found in the PATH are executed. If the -p option is given, the searchfor command is performed using a default value for PATH that is guaranteed to find all ofthe standard utilities. If either the -V or -v option is supplied, a description of command isprinted. The -v option causes a single word indicating the command or file name used toinvoke command to be displayed; the -V option produces a more verbose description. If the -Vor -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neitheroption is supplied and an error occurred or command cannot be found, the exit status is 127.Otherwise, the exit status of the command builtin is the exit status of command.

continue [n]

bash_man_page of 63

Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified,resume at the nth enclosing loop. n must be >= 1. If n is greater than the number of enclosingloops, the last enclosing loop (the ``top-level'' loop) is resumed. The return value is 0 unlessthe shell is not executing a loop when continue is executed.declare [-afFirx] [-p] [name[=value]]

typeset [-afFirx] [-p] [name[=value]]Declare variables and/or give them attributes. If no names are given then display the valuesof variables. The -p option will display the attributes and values of each name. When -p isused, additional options are ignored. The -F option inhibits the display of functiondefinitions; only the function name and attributes are printed. The -F option implies -f. Thefollowing options can be used to restrict output to variables with the specified attribute or togive variables attributes:-aEach name is an array variable (see Arrays above).-fUse function names only.-iThe variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION ) isperformed when the variable is assigned a value.-rMake names readonly. These names cannot then be assigned values by subsequentassignment statements or unset.-xMark names for export to subsequent commands via the environment.

Using `+' instead of `-' turns off the attribute instead, with the exception that +a may not beused to destroy an array variable. When used in a function, makes each name local, as withthe local command. The return value is 0 unless an invalid option is encountered, anattempt is made to define a function using "-f foo=bar", an attempt is made to assign a valueto a readonly variable, an attempt is made to assign a value to an array variable withoutusing the compound assignment syntax (see Arrays above), one of the names is not a validshell variable name, an attempt is made to turn off readonly status for a readonly variable,an attempt is made to turn off array status for an array variable, or an attempt is made todisplay a non-existent function with -f.

dirs [-clpv] [+n] [-n]Without options, displays the list of currently remembered directories. The default display ison a single line with directory names separated by spaces. Directories are added to the listwith the pushd command; the popd command removes entries from the list.+nDisplays the nth entry counting from the left of the list shown by dirs when invoked withoutoptions, starting with zero.-nDisplays the nth entry counting from the right of the list shown by dirs when invokedwithout options, starting with zero.-cClears the directory stack by deleting all of the entries.-lProduces a longer listing; the default listing format uses a tilde to denote the home directory.-pPrint the directory stack with one entry per line.-vPrint the directory stack with one entry per line, prefixing each entry with its index in thestack.

The return value is 0 unless an invalid option is supplied or n indexes beyond the end of thedirectory stack.

bash_man_page of 63

disown [-ar] [-h] [jobspec ...]Without options, each jobspec is removed from the table of active jobs. If the -h option isgiven, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent tothe job if the shell receives a SIGHUP. If no jobspec is present, and neither the -a nor the -roption is supplied, the current job is used. If no jobspec is supplied, the -a option means toremove or mark all jobs; the -r option without a jobspec argument restricts operation torunning jobs. The return value is 0 unless a jobspec does not specify a valid job.

echo [-neE] [arg ...]Output the args, separated by spaces, followed by a newline. The return status is always 0. If-n is specified, the trailing newline is suppressed. If the -e option is given, interpretation ofthe following backslash-escaped characters is enabled. The -E option disables theinterpretation of these escape characters, even on systems where they are interpreted bydefault. echo does not interpret -- to mean the end of options. echo interprets the followingescape sequences:\aalert (bell)\bbackspace\csuppress trailing newline\ean escape character\fform feed\nnew line\rcarriage return\thorizontal tab\vvertical tab\\backslash\nnnthe character whose ASCII code is the octal value nnn (one to three digits)\xnnnthe character whose ASCII code is the hexadecimal value nnn (one to three digits)

enable [-adnps] [-f filename] [name ...]Enable and disable builtin shell commands. Disabling a builtin allows a disk command whichhas the same name as a shell builtin to be executed with specifying a full pathname, eventhough the shell normally searches for builtins before disk commands. If -n is used, eachname is disabled; otherwise, names are enabled. For example, to use the test binary foundvia the PATH instead of the shell builtin version, run enable -n test. The -f option means toload the new builtin command name from shared object filename, on systems that supportdynamic loading. The -d option will delete a builtin previously loaded with -f. If no namearguments are given, or if the -p option is supplied, a list of shell builtins is printed. With noother option arguments, the list consists of all enabled shell builtins. If -n is supplied, onlydisabled builtins are printed. If -a is supplied, the list printed includes all builtins, with anindication of whether or not each is enabled. If -s is supplied, the output is restricted to thePOSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is aproblem loading a new builtin from a shared object.

eval [arg ...]The args are read and concatenated together into a single command. This command is thenread and executed by the shell, and its exit status is returned as the value of eval. If thereare no args, or only null arguments, eval returns 0.

exec [-cl] [-a name] [command [arguments]]

bash_man_page of 63

If command is specified, it replaces the shell. No new process is created. The argumentsbecome the arguments to command. If the -l option is supplied, the shell places a dash in thezeroth arg passed to command. This is what login(1) does. The -c option causes command tobe executed with an empty environment. If -a is supplied, the shell passes name as thezeroth argument to the executed command. If command cannot be executed for some reason,a non-interactive shell exits, unless the shell option execfail is enabled, in which case itreturns failure. An interactive shell returns failure if the file cannot be executed. If commandis not specified, any redirections take effect in the current shell, and the return status is 0. Ifthere is a redirection error, the return status is 1.

exit [n]Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the lastcommand executed. A trap on EXIT is executed before the shell terminates.export [-fn] [name[=word]] ...

export -pThe supplied names are marked for automatic export to the environment of subsequentlyexecuted commands. If the -f option is given, the names refer to functions. If no names aregiven, or if the -p option is supplied, a list of all names that are exported in this shell isprinted. The -n option causes the export property to be removed from the named variables.export returns an exit status of 0 unless an invalid option is encountered, one of the namesis not a valid shell variable name, or -f is supplied with a name that is not a function.fc [-e ename] [-nlr] [first] [last]

fc -s [pat=rep] [cmd]Fix Command. In the first form, a range of commands from first to last is selected from thehistory list. First and last may be specified as a string (to locate the last command beginningwith that string) or as a number (an index into the history list, where a negative number isused as an offset from the current command number). If last is not specified it is set to thecurrent command for listing (so that fc -l -10 prints the last 10 commands) and to firstotherwise. If first is not specified it is set to the previous command for editing and -16 forlisting.

The -n option suppresses the command numbers when listing. The -r option reverses theorder of the commands. If the -l option is given, the commands are listed on standard output.Otherwise, the editor given by ename is invoked on a file containing those commands. Ifename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDITis not set. If neither variable is set, vi is used. When editing is complete, the editedcommands are echoed and executed.

In the second form, command is re-executed after each instance of pat is replaced by rep. Auseful alias to use with this is r='fc -s', so that typing r cc runs the last command beginningwith cc and typing r re-executes the last command.

If the first form is used, the return value is 0 unless an invalid option is encountered or firstor last specify history lines out of range. If the -e option is supplied, the return value is thevalue of the last command executed or failure if an error occurs with the temporary file ofcommands. If the second form is used, the return status is that of the command re-executed,unless cmd does not specify a valid history line, in which case fc returns failure.

fg [jobspec]Resume jobspec in the foreground, and make it the current job. If jobspec is not present, theshell's notion of the current job is used. The return value is that of the command placed intothe foreground, or failure if run when job control is disabled or, when run with job controlenabled, if jobspec does not specify a valid job or jobspec specifies a job that was startedwithout job control.

getopts optstring name [args]getopts is used by shell procedures to parse positional parameters. optstring contains theoption letters to be recognized; if a letter is followed by a colon, the option is expected to havean argument, which should be separated from it by white space. Each time it is invoked,

bash_man_page of 63

getopts places the next option in the shell variable name, initializing name if it does notexist, and the index of the next argument to be processed into the variable OPTIND. OPTIND isinitialized to 1 each time the shell or a shell script is invoked. When an option requires anargument, getopts places that argument into the variable OPTARG. The shell does not resetOPTIND automatically; it must be manually reset between multiple calls to getopts withinthe same shell invocation if a new set of parameters is to be used.

When the end of options is encountered, getopts exits with a return value greater than zero.OPTIND is set to the index of the first non-option argument, and name is set to ?.

getopts normally parses the positional parameters, but if more arguments are given in args,getopts parses those instead.

getopts can report errors in two ways. If the first character of optstring is a colon, silenterror reporting is used. In normal operation diagnostic messages are printed when invalidoptions or missing option arguments are encountered. If the variable OPTERR is set to 0, noerror messages will be displayed, even if the first character of optstring is not a colon.

If an invalid option is seen, getopts places ? into name and, if not silent, prints an errormessage and unsets OPTARG. If getopts is silent, the option character found is placed inOPTARG and no diagnostic message is printed.

If a required argument is not found, and getopts is not silent, a question mark (?) is placedin name, OPTARG is unset, and a diagnostic message is printed. If getopts is silent, then acolon (:) is placed in name and OPTARG is set to the option character found.

getopts returns true if an option, specified or unspecified, is found. It returns false if the endof options is encountered or an error occurs.

hash [-r] [-p filename] [name]For each name, the full file name of the command is determined by searching the directoriesin $PATH and remembered. If the -p option is supplied, no path search is performed, andfilename is used as the full file name of the command. The -r option causes the shell to forgetall remembered locations. If no arguments are given, information about rememberedcommands is printed. The return status is true unless a name is not found or an invalidoption is supplied.

help [pattern]Display helpful information about builtin commands. If pattern is specified, help givesdetailed help on all commands matching pattern; otherwise help for all the builtins and shellcontrol structures is printed. The return status is 0 unless no command matches pattern.history [-c] [n]

history -anrw [filename]history -p arg [arg ...]history -s arg [arg ...]

With no options, display the command history list with line numbers. Lines listed with a *have been modified. An argument of n lists only the last n lines. If filename is supplied, it isused as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied,have the following meanings:-aAppend the ``new'' history lines (history lines entered since the beginning of the currentbash session) to the history file.-nRead the history lines not already read from the history file into the current history list.These are lines appended to the history file since the beginning of the current bash session.-rRead the contents of the history file and use them as the current history.

bash_man_page of 63

-wWrite the current history to the history file, overwriting the history file's contents.-cClear the history list by deleting all the entries.-pPerform history substitution on the following args and display the result on the standardoutput. Does not store the results in the history list. Each arg must be quoted to disablenormal history expansion.-sStore the args in the history list as a single entry. The last command in the history list isremoved before the args are added.

The return value is 0 unless an invalid option is encountered or an error occurs while readingor writing the history file.

jobs [-lnprs] [ jobspec ... ]jobs -x command [ args ... ]

The first form lists the active jobs. The options have the following meanings:-lList process IDs in addition to the normal information.-pList only the process ID of the job's process group leader.-nDisplay information only about jobs that have changed status since the user was last notifiedof their status.-rRestrict output to running jobs.-sRestrict output to stopped jobs.

If jobspec is given, output is restricted to information about that job. The return status is 0unless an invalid option is encountered or an invalid jobspec is supplied.

If the -x option is supplied, jobs replaces any jobspec found in command or args with thecorresponding process group ID, and executes command passing it args, returning its exitstatus.

kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...kill -l [sigspec | exit_status]

Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspecis either a signal name such as SIGKILL or a signal number; signum is a signal number. Ifsigspec is a signal name, the name may be given with or without the SIG prefix. If sigspec isnot present, then SIGTERM is assumed. An argument of -l lists the signal names. If anyarguments are supplied when -l is given, the names of the signals corresponding to thearguments are listed, and the return status is 0. The exit_status argument to -l is a numberspecifying either a signal number or the exit status of a process terminated by a signal. killreturns true if at least one signal was successfully sent, or false if an error occurs or aninvalid option is encountered.

let arg [arg ...]Each arg is an arithmetic expression to be evaluated (see ARITHMETICEVALUATION). If the lastarg evaluates to 0, let returns 1; 0 is returned otherwise.

local [name[=value] ...]For each argument, a local variable named name is created, and assigned value. When localis used within a function, it causes the variable name to have a visible scope restricted tothat function and its children. With no operands, local writes a list of local variables to thestandard output. It is an error to use local when not within a function. The return status is 0unless local is used outside a function, or an invalid name is supplied.

bash_man_page of 63

logoutExit a login shell.

popd [-n] [+n] [-n]Removes entries from the directory stack. With no arguments, removes the top directoryfrom the stack, and performs a cd to the new top directory. Arguments, if supplied, have thefollowing meanings:+nRemoves the nth entry counting from the left of the list shown by dirs, starting with zero.For example: ``popd +0'' removes the first directory, ``popd +1'' the second.-nRemoves the nth entry counting from the right of the list shown by dirs, starting with zero.For example: ``popd -0'' removes the last directory, ``popd -1'' the next to last.-nSuppresses the normal change of directory when removing directories from the stack, so thatonly the stack is manipulated.

If the popd command is successful, a dirs is performed as well, and the return status is 0.popd returns false if an invalid option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails.

printf format [arguments]Write the formatted arguments to the standard output under the control of the format. Theformat is a character string which contains three types of objects: plain characters, which aresimply copied to standard output, character escape sequences, which are converted andcopied to the standard output, and format specifications, each of which causes printing of thenext successive argument. In addition to the standard printf(1) formats, %b causes printf toexpand backslash escape sequences in the corresponding argument, and %q causes printf tooutput the corresponding argument in a format that can be reused as shell input.

The format is reused as necessary to consume all of the arguments. If the format requiresmore arguments than are supplied, the extra format specifications behave as if a zero valueor null string, as appropriate, had been supplied.

pushd [-n] [dir]pushd [-n] [+n] [-n]

Adds a directory to the top of the directory stack, or rotates the stack, making the new top ofthe stack the current working directory. With no arguments, exchanges the top twodirectories and returns 0, unless the directory stack is empty. Arguments, if supplied, havethe following meanings:+nRotates the stack so that the nth directory (counting from the left of the list shown by dirs,starting with zero) is at the top.-nRotates the stack so that the nth directory (counting from the right of the list shown by dirs,starting with zero) is at the top.-nSuppresses the normal change of directory when adding directories to the stack, so that onlythe stack is manipulated.dirAdds dir to the directory stack at the top, making it the new current working directory.

If the pushd command is successful, a dirs is performed as well. If the first form is used,pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless thedirectory stack is empty, a non-existent directory stack element is specified, or the directorychange to the specified new current directory fails.

pwd [-LP]

bash_man_page of 63

Print the absolute file name of the current working directory. The file name printed containsno symbolic links if the -P option is supplied or the -o physical option to the set builtincommand is enabled. If the -L option is used, symbolic links are followed. The return statusis 0 unless an error occurs while reading the name of the current directory or an invalidoption is supplied.

read [-er] [-a aname] [-p prompt] [name ...]One line is read from the standard input, and the first word is assigned to the first name, thesecond word to the second name, and so on, with leftover words and their interveningseparators assigned to the last name. If there are fewer words read from the standard inputthan names, the remaining names are assigned empty values. The characters in IFS are usedto split the line into words. Options, if supplied, have the following meanings:-rA backslash-newline pair is not ignored, and the backslash is considered to be part of theline.-pDisplay prompt, without a trailing newline, before attempting to read any input. The promptis displayed only if input is coming from a terminal.-aThe words are assigned to sequential indices of the array variable aname, starting at 0.aname is unset before any new values are assigned. Other name arguments are ignored.-eIf the standard input is coming from a terminal, readline (see READLINE above) is used toobtain the line.

If no names are supplied, the line read is assigned to the variable REPLY. The return code iszero, unless end-of-file is encountered.

readonly [-apf] [name ...]The given names are marked readonly; the values of these names may not be changed bysubsequent assignment. If the -f option is supplied, the functions corresponding to the namesare so marked. The -a option restricts the variables to arrays. If no name arguments aregiven, or if the -p option is supplied, a list of all readonly names is printed. The -p optioncauses output to be displayed in a format thatmay be reused as input. The return status is 0unless an invalid option is encountered, one of the names is not a valid shell variable name,or -f is supplied with a name that is not a function.

return [n]Causes a function to exit with the return value specified by n. If n is omitted, the returnstatus is that of the last command executed in the function body. If used outside a function,but during execution of a script by the . (source) command, it causes the shell to stopexecuting that script and return either n or the exit status of the last command executedwithin the script as the exit status of the script. If used outside a function and not duringexecution of a script by ., the return status is false.

set [--abefhkmnptuvxBCHP] [-o option] [arg ...]Without options, the name and value of each shell variable are displayed in a format that canbe reused as input. The output is sorted according to the current locale. When options arespecified, they set or unset shell attributes. Any arguments remaining after the options areprocessed are treated as values for the positional parameters and are assigned, in order, to$1, $2, ... $n. Options, if specified, have the following meanings:-aAutomatically mark variables which are modified or created for export to the environment ofsubsequent commands.-bReport the status of terminated background jobs immediately, rather than before the nextprimary prompt. This is effective only when job control is enabled.-eExit immediately if a simple command (see SHELL GRAMMAR above) exits with a non-zerostatus. The shell does not exit if the command that fails is part of an until or while loop, part

bash_man_page of 63

of an if statement, part of a && or || list, or if the command's return value is being invertedvia !.-fDisable pathname expansion.-hRemember the location of commands as they are looked up for execution. This is enabled bydefault.-kAll arguments in the form of assignment statements are placed in the environment for acommand, not just those that precede the command name.-mMonitor mode. Job control is enabled. This option is on by default for interactive shells onsystems that support it (see JOB CONTROL above). Background processes run in a separateprocess group and a line containing their exit status is printed upon their completion.-nRead commands but do not execute them. This may be used to check a shell script for syntaxerrors. This is ignored by interactive shells.-o option-nameThe option-name can be one of the following:allexportSame as -a.braceexpandSame as -B.emacsUse an emacs-style command line editing interface. This is enabled by default when the shellis interactive, unless the shell is started with the --noediting option.errexitSame as -e.hashallSame as -h.histexpandSame as -H.historyEnable command history, as described above under HISTORY. This option is on by default ininteractive shells.ignoreeofThe effect is as if the shell command IGNOREEOF=10 had been executed (see ShellVariables above).keywordSame as -k.monitorSame as -m.noclobberSame as -C.noexecSame as -n.noglobSame as -f.notifySame as -b.nounsetSame as -u.onecmdSame as -t.physicalSame as -P.posix

bash_man_page of 63

Change the behavior of bash where the default operation differs from the POSIX 1003.2standard to match the standard.privilegedSame as -p.verboseSame as -v.viUse a vi-style command line editing interface.xtraceSame as -x.

If -o is supplied with no option-name, the values of the current options are printed. If +o issupplied with no option-name, a series of set commands to recreate the current optionsettings is displayed on the standard output.

-pTurn on privileged mode. In this mode, the $ENV file is not processed, shell functions are notinherited from the environment, and the variable The SHELLOPTS variable, if it appearsin the environment, is ignored. This is enabled automatically on startup if the effective user(group) id is not equal to the real user (group) id. Turning this option off causes the effectiveuser and group ids to be set to the real user and group ids.-tExit after reading and executing one command.-uTreat unset variables as an error when performing parameter expansion. If expansion isattempted on an unset variable, the shell prints an error message, and, if not interactive,exits with a non-zero status.-vPrint shell input lines as they are read.-xAfter expanding each simple command, display the expanded value of PS4, followed by thecommand and its expanded arguments.-BThe shell performs brace expansion (see Brace Expansion above). This is on by default.-CIf set, bash does not overwrite an existing file with the >, >&, and <> redirection operators.This may be overridden when creating output files by using the redirection operator >|instead of >.-HEnable ! style history substitution. This option is on by default when the shell is interactive.-PIf set, the shell does not follow symbolic links when executing commands such as cd thatchange the current working directory. It uses the physical directory structure instead. Bydefault, bash follows the logical chain of directories when performing commands whichchange the current directory.--If no arguments follow this option, then the positional parameters are unset. Otherwise, thepositional parameters are set to the args, even if some of them begin with a -.-Signal the end of options, cause all remaining args to be assigned to the positionalparameters. The -x and -v options are turned off. If there are no args, the positionalparameters remain unchanged.

The options are off by default unless otherwise noted. Using + rather than - causes theseoptions to be turned off. The options can also be specified as arguments to an invocation ofthe shell. The current set of options may be found in $-. The return status is always trueunless an invalid option is encountered.

bash_man_page of 63

shift [n]The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by thenumbers $# down to $#-n+1 are unset. n must be a non-negative number less than or equalto $#. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. If n isgreater than $#, the positional parameters are not changed. The return status is greaterthan zero if n is greater than $# or less than zero; otherwise 0.

shopt [-pqsu] [-o] [optname ...]Toggle the values of variables controlling optional shell behavior. With no options, or withthe -p option, a list of all settable options is displayed, with an indication of whether or noteach is set. The -p option causes output to be displayed in a form that may be reused asinput. Other options have the following meanings:-sEnable (set) each optname.-uDisable (unset) each optname.-qSuppresses normal output (quiet mode); the return status indicates whether the optname isset or unset. If multiple optname arguments are given with -q, the return status is zero if alloptnames are enabled; non-zero otherwise.-oRestricts the values of optname to be those defined for the -o option to the set builtin.

If either -s or -u is used with no optname arguments, the display is limited to those optionswhich are set or unset, respectively. Unless otherwise noted, the shopt options are disabled(unset) by default.

The return status when listing options is zero if all optnames are enabled, non-zerootherwise. When setting or unsetting options, the return status is zero unless an optname isnot a valid shell option.

The list of shopt options is:

cdable_varsIf set, an argument to the cd builtin command that is not a directory is assumed to be thename of a variable whose value is the directory to change to.cdspellIf set, minor errors in the spelling of a directory component in a cd command will becorrected. The errors checked for are transposed characters, a missing character, and onecharacter too many. If a correction is found, the corrected file name is printed, and thecommand proceeds. This option is only used by interactive shells.checkhashIf set, bash checks that a command found in the hash table exists before trying to execute it.If a hashed command no longer exists, a normal path search is performed.checkwinsizeIf set, bash checks the window size after each command and, if necessary, updates thevalues of LINES and COLUMNS.cmdhistIf set, bash attempts to save all lines of a multiple-line command in the same history entry.This allows easy re-editing of multi-line commands.dotglobIf set, bash includes filenames beginning with a `.' in the results of pathname expansion.execfailIf set, a non-interactive shell will not exit if it cannot execute the file specified as anargument to the exec builtin command. An interactive shell does not exit if exec fails.expand_aliasesIf set, aliases are expanded as described above under ALIASES. This option is enabled bydefault for interactive shells.

bash_man_page of 63

extglobIf set, the extended pattern matching features described above under PathnameExpansion are enabled.histappendIf set, the history list is appended to the file named by the value of the HISTFILE variablewhen the shell exits, rather than overwriting the file.histreeditIf set, and readline is being used, a user is given the opportunity to re-edit a failed historysubstitution.histverifyIf set, and readline is being used, the results of history substitution are not immediatelypassed to the shell parser. Instead, the resulting line is loaded into the readline editingbuffer, allowing further modification.hostcompleteIf set, and readline is being used, bash will attempt to perform hostname completion whena word containing a @ is being completed (see Completing under READLINE above). This isenabled by default.huponexitIf set, bash will send SIGHUP to all jobs when an interactive login shell exits.interactive_commentsIf set, allow a word beginning with # to cause that word and all remaining characters on thatline to be ignored in an interactive shell (see COMMENTS above). This option is enabled bydefault.lithistIf set, and the cmdhist option is enabled, multi-line commands are saved to the history withembedded newlines rather than using semicolon separators where possible.mailwarnIf set, and a file that bash is checking for mail has been accessed since the last time it waschecked, the message ``The mail in mailfile has been read'' is displayed.nocaseglobIf set, bash matches filenames in a case-insensitive fashion when performing pathnameexpansion (see Pathname Expansion above).nullglobIf set, bash allows patterns which match no files (see Pathname Expansion above) toexpand to a null string, rather than themselves.promptvarsIf set, prompt strings undergo variable and parameter expansion after being expanded asdescribed in PROMPTING above. This option is enabled by default.shift_verboseIf set, the shift builtin prints an error message when the shift count exceeds the number ofpositional parameters.sourcepathIf set, the source (.) builtin uses the value of PATH to find the directory containing the filesupplied as an argument. This option is enabled by default.

suspend [-f]Suspend the execution of this shell until it receives a SIGCONT signal. The -f option says notto complain if this is a login shell; just suspend anyway. The return status is 0 unless theshell is a login shell and -f is not supplied, or if job control is not enabled.test expr

[ expr ]Return a status of 0 or 1 depending on the evaluation of the conditional expression expr.Each operator and operand must be a separate argument. Expressions are composed of theprimaries described above under CONDITIONALEXPRESSIONS.

Expressions may be combined using the following operators, listed in decreasing order ofprecedence.

! expr

bash_man_page of 63

True if expr is false.( expr )Returns the value of expr. This may be used to override the normal precedence of operators.expr1 -a expr2True if both expr1 and expr2 are true.expr1 -o expr2True if either expr1 or expr2 is true.

test and [ evaluate conditional expressions using a set of rules based on the number ofarguments.

0 argumentsThe expression is false.1 argumentThe expression is true if and only if the argument is not null.2 argumentsIf the first argument is !, the expression is true if and only if the second argument is null. Ifthe first argument is one of the unary conditional operators listed above underCONDITIONALEXPRESSIONS, the expression is true if the unary test is true. If the first argumentis not a valid unary conditional operator, the expression is false.3 argumentsIf the second argument is one of the binary conditional operators listed above underCONDITIONALEXPRESSIONS, the result of the expression is the result of the binary test usingthe first and third arguments as operands. If the first argument is !, the value is the negationof the two-argument test using the second and third arguments. If the first argument isexactly ( and the third argument is exactly ), the result is the one-argument test of thesecond argument. Otherwise, the expression is false. The -a and -o operators are consideredbinary operators in this case.4 argumentsIf the first argument is !, the result is the negation of the three-argument expressioncomposed of the remaining arguments. Otherwise, the expression is parsed and evaluatedaccording to precedence using the rules listed above.5 or more argumentsThe expression is parsed and evaluated according to precedence using the rules listed above.

timesPrint the accumulated user and system times for the shell and for processes run from theshell. The return status is 0.

trap [-lp] [arg] [sigspec ...]The command arg is to be read and executed when the shell receives signal(s) sigspec. If argis absent or -, all specified signals are reset to their original values (the values they had uponentrance to the shell). If arg is the null string the signal specified by each sigspec is ignoredby the shell and by the commands it invokes. If arg is -p then the trap commands associatedwith each sigspec are displayed. If no arguments are supplied or if only -p is given, trapprints the list of commands associated with each signal number. Each sigspec is either asignal name defined in <signal.h>, or a signal number. If a sigspec is EXIT (0) the commandarg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is executedafter every simple command (see SHELL GRAMMAR above). The -l option causes the shell toprint a list of signal names and their corresponding numbers. Signals ignored upon entry tothe shell cannot be trapped or reset. Trapped signals are reset to their original values in achild process when it is created. The return status is false if any sigspec is invalid; otherwisetrap returns true.

type [-atp] name [name ...]With no options, indicate how each name would be interpreted if used as a command name. Ifthe -t option is used, type prints a string which is one of alias, keyword, function, builtin, orfile if name is an alias, shell reserved word, function, builtin, or disk file, respectively. If thename is not found, then nothing is printed, and an exit status of false is returned. If the -poption is used, type either returns the name of the disk file that would be executed if namewere specified as a command name, or nothing if type -t name would not return file. If a

bash_man_page of 63

command is hashed, -p prints the hashed value, not necessarily the file that appears first inPATH. If the -a option is used, type prints all of the places that contain an executable namedname. This includes aliases and functions, if and only if the -p option is not also used. Thetable of hashed commands is not consulted when using -a. type returns true if any of thearguments are found, false if none are found.

ulimit [-SHacdflmnpstuv [limit]]Provides control over the resources available to the shell and to processes started by it, onsystems that allow such control. The value of limit can be a number in the unit specified forthe resource, or the value unlimited. The -H and -S options specify that the hard or softlimit is set for the given resource. A hard limit cannot be increased once it is set; a soft limitmay be increased up to the value of the hard limit. If neither -H nor -S is specified, both thesoft and hard limits are set. If limit is omitted, the current value of the soft limit of theresource is printed, unless the -H option is given. When more than one resource is specified,the limit name and unit are printed before the value. Other options are interpreted asfollows:-aAll current limits are reported-cThe maximum size of core files created-dThe maximum size of a process's data segment-fThe maximum size of files created by the shell-lThe maximum size that may be locked into memory-mThe maximum resident set size-nThe maximum number of open file descriptors (most systems do not allow this value to beset)-pThe pipe size in 512-byte blocks (this may not be set)-sThe maximum stack size-tThe maximum amount of cpu time in seconds-uThe maximum number of processes available to a single user-vThe maximum amount of virtual memory available to the shell

If limit is given, it is the new value of the specified resource (the -a option is display only). Ifno option is given, then -f is assumed. Values are in 1024-byte increments, except for -t,which is in seconds, -p, which is in units of 512-byte blocks, and -n and -u, which areunscaled values. The return status is 0 unless an invalid option is encountered, a non-numeric argument other than unlimited is supplied as limit, or an error occurs whilesetting a new limit.

umask [-p] [-S] [mode]The user file-creation mask is set to mode. If mode begins with a digit, it is interpreted as anoctal number; otherwise it is interpreted as a symbolic mode mask similar to that acceptedby chmod(1). If mode is omitted, or if the -S option is supplied, the current value of the maskis printed. The -S option causes the mask to be printed in symbolic form; the default outputis an octal number. If the -p option is supplied, and mode is omitted, the output is in a formthat may be reused as input. The return status is 0 if the mode was successfully changed or ifno mode argument was supplied, and false otherwise.

unalias [-a] [name ...]

bash_man_page of 63

Remove names from the list of defined aliases. If -a is supplied, all alias definitions areremoved. The return value is true unless a supplied name is not a defined alias.

unset [-fv] [name ...]For each name, remove the corresponding variable or function. If no options are supplied, orthe -v option is given, each name refers to a shell variable. Read-only variables may not beunset. If -f is specifed, each name refers to a shell function, and the function definition isremoved. Each unset variable or function is removed from the environment passed tosubsequent commands. If any of RANDOM, SECONDS, LINENO, HISTCMD, or DIRSTACK are unset,they lose their special properties, even if they are subsequently reset. The exit status is trueunless a name does not exist or is readonly.

wait [n]Wait for the specified process and return its termination status. n may be a process ID or ajob specification; if a job spec is given, all processes in that job's pipeline are waited for. If n isnot given, all currently active child processes are waited for, and the return status is zero. Ifn specifies a non-existent process or job, the return status is 127. Otherwise, the returnstatus is the exit status of the last process or job waited for.

RESTRICTED SHELLIf bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomesrestricted. A restricted shell is used to set up an environment more controlled than the standardshell. It behaves identically to bash with the exception that the following are disallowed or notperformed:

*changing directories with cd

*setting or unsetting the values of SHELL or PATH

*specifying command names containing /

*specifying a file name containing a / as an argument to the . builtin command

*importing function definitions from the shell environment at startup

*parsing the value of SHELLOPTS from the shell environment at startup

*redirecting output using the >, >|, <>, >&, &>, and >> redirection operators

*using the exec builtin command to replace the shell with another command

*adding or deleting builtin commands with the -f and -d options to the enable builtincommand

*specifying the -p option to the command builtin command

*turning off restricted mode with set +r or set +o restricted.

These restrictions are enforced after any startup files are read.

When a command that is found to be a shell script is executed (see COMMAND EXECUTION above),rbash turns off any restrictions in the shell spawned to execute the script.

SEE ALSO

bash_man_page of 63

Bash Features, Brian Fox and Chet RameyThe Gnu Readline Library, Brian Fox and Chet RameyThe Gnu History Library, Brian Fox and Chet RameyPortable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEEsh(1), ksh(1), csh(1)emacs(1), vi(1)readline(3)

FILES/bin/bash

The bash executable/etc/profile

The systemwide initialization file, executed for login shells~/.bash_profile

The personal initialization file, executed for login shells~/.bashrc

The individual per-interactive-shell startup file~/.inputrc

Individual readline initialization file

AUTHORSBrian Fox, Free Software [email protected]

Chet Ramey, Case Western Reserve [email protected]

BUG REPORTSIf you find a bug in bash, you should report it. But first, you should make sure that it really is a bug,and that it appears in the latest version of bash that you have.

Once you have determined that a bug actually exists, use the bashbug command to submit a bugreport. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bugreports may be mailed to [email protected] or posted to the Usenet newsgroup gnu.bash.bug.

ALL bug reports should include:

The version number of bashThe hardware and operating systemThe compiler used to compileA description of the bug behaviourA short script or `recipe' which exercises the bug

bashbug inserts the first three items automatically into the template it provides for filing a bugreport.

Comments and bug reports concerning this manual page should be directed to [email protected].

bash_man_page of 63

BUGSIt's too big and too slow.

There are some subtle differences between bash and traditional versions of sh, mostly because of thePOSIX specification.

Aliases are confusing in some uses.

Shell builtin commands and functions are not stoppable/restartable.

Compound commands and command sequences of the form `a ; b ; c' are not handled gracefully whenprocess suspension is attempted. When a process is stopped, the shell immediately executes the nextcommand in the sequence. It suffices to place the sequence of commands between parentheses toforce it into a subshell, which may be stopped as a unit.

Commands inside of $(...) command substitution are not parsed until substitution is attempted. Thiswill delay error reporting until some time after the command is entered.

Array variables may not (yet) be exported.

IndexNAMESYNOPSISCOPYRIGHTDESCRIPTIONOPTIONSARGUMENTSINVOCATIONDEFINITIONSRESERVED WORDSSHELL GRAMMAR

Simple CommandsPipelinesListsCompound Commands

COMMENTSQUOTINGPARAMETERS

Positional ParametersSpecial ParametersShell VariablesArrays

EXPANSIONBrace ExpansionTilde ExpansionParameter ExpansionCommand SubstitutionArithmetic ExpansionProcess Substitution

bash_man_page of 63

Word SplittingPathname ExpansionQuote Removal

REDIRECTIONRedirecting InputRedirecting OutputAppending Redirected OutputRedirecting Standard Output and Standard ErrorHere DocumentsDuplicating File DescriptorsOpening File Descriptors for Reading and Writing

ALIASESFUNCTIONSARITHMETIC EVALUATIONCONDITIONAL EXPRESSIONSSIMPLE COMMAND EXPANSIONCOMMAND EXECUTIONCOMMAND EXECUTION ENVIRONMENTENVIRONMENTEXIT STATUSSIGNALSJOB CONTROLPROMPTINGREADLINE

Readline NotationReadline InitializationReadline Key BindingsReadline VariablesReadline Conditional ConstructsSearchingReadline Command NamesCommands for MovingCommands for Manipulating the HistoryCommands for Changing TextKilling and YankingNumeric ArgumentsCompletingKeyboard MacrosMiscellaneous

HISTORYHISTORY EXPANSION

Event DesignatorsWord DesignatorsModifiers

SHELL BUILTIN COMMANDSRESTRICTED SHELLSEE ALSOFILESAUTHORSBUG REPORTSBUGS

This document was created by man2html using the manual pages.Time: 23:38:45 GMT, June 20, 1998

bash.htmlTutorials - udel.eduudel.edu/~weiher/pdf/bash.pdf · bash_man_page Page 2 of 63 If the -i...

Documents

Transcript of bash.htmlTutorials - udel.eduudel.edu/~weiher/pdf/bash.pdf · bash_man_page Page 2 of 63 If the -i...